Dogs do scale with your hp and defenses (think it was 1.0.4 where that change was made). There are also talents where they can use your regen/thorns as well. High IAS is not necessary for sure. We could debate whether it is more optimal but it's definitely not necessary.
High attack speed isn't that good for us. I stay alive with LS from my weapon, If I go OOM fast, I can't get enough life and die. Since we have limited resources, the damage you deal will always be the same whatever your attack speed be.