Ah, foo. I could do it two days ago (sort of), but I guess that was a bug.
Well, poo. I guess my dark woods full of dangerous wolves idea is all shot to heck now.
I tried the longer ticks thing, too, but with wolves. Doesn't seem to make a difference. They go docile pretty much immediately, even though a player in survival mode is in sight. They will go after skeletons, though.
I wish/hope there's a way to make them go after players – otherwise they're not too useful to spawn.
Unfortunately, the aggro'd wolves don't see a survival-mode player as a target. Which is the main reason I want to summon them.
Addition: Also sometimes crashes the game. Not sure what is different when it crashes or not.
Thanks!