*flips open National Geographic: Sanctuary Edition*
Treasure goblins are highly trained professionals, specializing in the transportation of valuable goods throughout the dangerous lands of Sanctuary. They are particularly skilled at engaging evasive maneuvers when avoiding the hostilities of local Nephalem. Though the reward may be great, one must be cautious in approaching the timid and excitable Treasure Goblin, lest you find yourself guided through a gauntlet of dangerous elite packs.
In summary, yes, % Bonus Damage to Elites applies to Treasure Goblins. ;P