Starcraft II, Heart of the Swarm.
While playing "Death from above", I couldn't help but notice a couple vikings slacking off:
As far as I am concerned, they never actually attack me. They just sit there watching the show. I'm not entirely sure if this makes any difference depending on the difficulty.
I didn't bother attacking them. And they sure didn't bother harassing me either.
Now then, obviously they're very clever terrans for not bugging The Swarm, but, do they play any role other than troll their comrades?