here's my guide for the support DH, aimed at assuming the role of the support WD in the current 4man meta (ET Wizard + 3x Support). After my initial Tier 98 clear on nonseason from a couple days ago I have optimized the build a little bit further and tested out different options and this is the final result which I think will work best for most purposes. From the testing so far it seems both classes are about even for both speedruns and pushing, meaning this build is viable up to and beyond Tier 100, with some advantages and disadvantages on both sides. For the most part, DH provides slightly less damage buffs but makes up for it with better consistency on bad RGs (globespawn) and much better pulling due to the high mobility. DH also has the big advantage of creating less lag than the WD (because we don't use DoT effects), so you can play 4man with a DH at prime time with much less trouble (obviously it doesn't completely fix the issue), and even use Pain Enhancer on the Wizard when playing during hours of low server load.
First off, we take all the damage buffs we can get: Multishot - Wind Chill (15% CHC), Marked for Death - Contagion (20% DIBS), Calamity (20% DIBS; stacks with MfD), Strongarm Bracers (30% DIBS, triggered by Vault - Rattling Roll); Wolf Companion (30% DIBS). We combine this with Sentry - Guardian Turret (25% Shield) and Numbing Traps (25% reduced damage done, triggered by Wind Chill and Sentries) for a total of 43.75% damage reduction (stacking multiplicitavely). On top of that, we use Iceblink (10% CHC, triggered by Wind Chill). The remaining passives are Tactical Advantage, Awareness, Blood Vengeance, Single Out (Hellfire). Alls these buffs are in the additive DIBS (Damage Increased By Skills) category (not counting CHC from Wind Chill), which can add up to 100%, but more realistically it will be an average of ~70-80% (some monsters can't be knockbacked / you won't be close enough to to so all the time / MfD needs time to spread etc.). Oculus Ring is a separate multiplier for another up to 85% bonus.
Ball Lightning will be used to proc globes via the cubed Solanium, which is very important on single target Rift Guardians where the Barb alone can't spawn enough. Depending on positioning and the hitbox size, you can expect to spawn around 1 health globe per 5-8 seconds per target.
Most of the items can be replaced because they don't provide mandatory bonuses but there are some you should definitely have: Aquila Cuirass, Illusory Boots, Oculus Ring, Obsidian Ring, St. Archew's Gage, Calamity, Meticulous Bolts, Corruption (crafted), Leoric's Crown or Pride's Fall, Krelm's Buff Belt or String of Ears or Insatiable Belt (a3 bounties). There are no special pants to use and they removed the 5th primary from Hammer Jammers so just use whichever you have with good rolls. A Hellfire Amulet is recommended to make reaching the 100% CHC easier, you will need only 40% from items and paragons with the Single Out passive (25% SO, 15% WC, 10% IB, 10% Ancients). You need to wear either Nemesis Bracers or Strongarm Bracers and cube the other, Barb and Monk don't have a slot to waste on these. Immunity amulets could be okay but usually you will die from physical damage, not elemental damage. Ess of Johan and Overwhelming Desire are not recommended because they will screw up the pulls, same with M2 + Zoey's Secret (pets blocking monsters or RG).
Stat priorities are 40% CHC > RCR > IAS > Defense > CDR. I recommend to run CDR on only Obsidian Ring and drop CHC from both rings as well as either gloves or amulet. You should have at least 12-15 yards pickup radius to make picking the globes easier, especially on RG fights where you sometimes have to avoid any movement to not risk screwing up the positioning. Try to balance your armor and allres in a 10:1 ratio for optimal defense.
For a support role, the DH proves to be very active and engaging. You have 5 main objectives during a rift:
1) Guiding the group to the elite packs
2) Scouting for pylon spawns (and clicking them) at the right time
3) Pulling more monsters while keeping up the damage / defense buffs for the Wizard
4) Spawning globes on single target RGs
5) Saving the last pylon of the rift for the RG and dragging the pack to the group once the RG is in a good spot
Since the meta so far has been defined by a support WD and most people are usually slow to adapt new ideas such as the Sup DH, you have to give them a reason to keep inviting you over a WD, and the best way to do that is to capitalize on what a DH can do best: Move around and be awesome. With Tactical Advantage, Vault and Krelm's Belt we have an incredible movement speed and use that to pull monsters from all directions while still staying nearby the group to provide our buffs most of the time. Ball Lightning is a perfect spell for pulling, it travels slowly and keeps zapping the enemies so they stay aggro'd as long as you don't move too far away, make sure you don't Multishot stuff you want to pull because they will be incredibly slow then. Using pylons at the right time can be crucial because sometimes you want to stack everything right on top of the pylon or move away from it to stack everything in a corner, in any case you should avoid vaulting away from a pack to not stack diminishing returns for harpoon on them. What's important for bringing a pack to the RG: Don't move too far away or it will despawn, so try to keep it on the edge of the screen. If your wolf is blocking the RG, you can teleport to town for a second to despawn it so that the group can get the RG into a corner properly.
Try to set up your two sentries as early as possible to ensure permanent uptime of the shield. With some practice you will know where the Wizard wants to stay and it will be really easy because they usually don't move much after they found a spot. Since we use Marked for Death - Contagion you need to snipe a low hp target at the beginning of a fight to make sure it spreads to everything quickly afterwards. You know you got the right target by looking at the enemy's hp bar at the top of your screen (MfD target-locks for ~half a second on cast). Make sure you reset your Wolf Companion via Obsidian Ring in time to keep it up 100% of the time, with ~18-19% CDR it will take a couple hits to get the CD sufficiently low. Also don't shoot your Ball Lightning into packs of more than 15 monsters because you will instantly lag out the game (combined with the Wizard), you can use it freely for pulling and spawning globes in other situations though. Strongarm Bracers cannot be kept up all the time but you can still try to vault through the stacked packs once in a while to debuff them, other than that you should constantly be on the move and hunt for more monsters to pull towards the group, and run back and forth to keep monsters following. Make sure you still keep up Sentries and Wind Chill all the time.
Some secondary objectives depending on time of day, rift composition and group members:
a) Avoid creating laggy situations by overpulling
Communicate with the Barb to tell him when he needs to harpoon the monsters following you
c) Avoid controlling the monsters you engage to make sure they can be harpooned (especially try to not him them with Vault)
d) Drag along leftover monsters / elites to the next pack
e) Stay alive
This is pretty straightforward but I wanted to mention this regardless. Some rifts are so dense that you will lag no matter what, so in some situations it might be okay to vault through monsters and make sure they stop following / can't be harpooned. Other than that, always tell your Barb where you are going and when he should start harpooning in that direction, that way you can speed up the pulls a lot on many monster types. On some monster types you can also drag along elite packs easily via Ball Lightning, so instead of running in front you will follow the rest of the group and keep the pack engaged (e.g. Ghosts or Winged Assassins). As a DH it can be tough to survive sometimes because for most of the rift you're on your own and you have unusually low toughness for a support character, so good reactions and movement are required. You very often drop Ignore Pain and Aquila Cuirass and without M2 / Zoey's Secret you will definitely fall below 1b toughness in many situations, which will make you a squishy target on Tier 90+. Therefore, to keep up the Elusive Ring buff as much as possible either by vaulting before you engage new monsters or by vaulting into a orthogonal direction to not hit them but also don't de-aggro them.
To see more about the build in action, consider watching the video.
Some variations you can use for optimizing certain aspects of the build:
1) Entangling Shot + Odyssey's End (cubed) instead of Ball Lightning. 25% more DIBS at the cost of good pulls and globe spawn, can be used for fishing on high tiers.
2) Hungering Arrow + Ninth Sirri Catchel instead of Ball Lightning. Spawns slightly more globes on single target. I wouldn't recommend that setup but it's an option if your group is having big trouble with these pesky Rift Guardians.
3) LoN + Spike Traps - Echoing Blast. For extreme fishing you can drop Vault and Elusive Ring and use LoN for the toughness. You can get 20% more DIBS from the Spike Traps (the freeze is not required to apply the buff).
4) Toxin gem instead of Gogok. 10% more DIBS for more lags and less globes on RG.
Enjoy playing your DH in groups =)
Update 18 Feb:
During the last couple of weeks I managed to optimize the Sup DH setup a little, especially for higher tiers / no boss runs were you are not required to spawn globes. I included the UE 4-piece (shoulders, gloves, pants, chest) for the damage reduction, dropped Corruption + St Archew's and cubed Aquila. I dropped Ball Lightning for Entangling Shot - Chain Gang and Solanium for Odyssey's End, like that you can easily stack up 25% more additive damage on everything in a matter of seconds, plus it enables you to use Wraps of Clarity (when you don't need to run Nemesis, or you drop Leoric's Crown for UE helm). Because we don't need a quiver anymore, I went for dual-wielding and added the Fortress Ballista, another decent choice would be the Bombardier's Rucksack. I also dropped the Gogok of Swiftness for Moratium, which helps to survive heavy attacks (and most importantly works against physical attacks). The additional toughness will make the DH almost invincible even without augments, that way you can pull and facetank dangerous attack for the Wizard much more aggressively. I also dropped Strongarm Bracers and Vault - Rattling Roll entirely, since everything is pretty much permanently immune as soon as they enter the fight. I use Action Shot instead for easier pulling.
Since I don't need critical hit chance, I dropped all of it in favor of more attack speed and resource cost reduction, which helps especially for skipping, scouting and aggroing. Without the Ball Lightning you can have trouble pulling enemies properly on some monster combos, but usually 1-2 well-placed Entangling Shots or Vault - Action Shot + faceaggro will do the job, too. Pro tip: Watch your Nephalem Glory stacks, the chain lightning proc will easily aggro whole packs of monsters with a single Entangling Shot most of the time.
D3planner link for high tiers: http://www.d3planner.com/539640913