Actually we just deal more aggro than Shadow Priests, they invest in wide variety of -aggro talents and can't be expected to respec to PvE uselessness just for the emp fight. Ours aren't passive. Searing Pain is a high aggro move with no cooldown, unlike Mind Blast

Doesn't need to be soul link, it's master demonology that helps. That gives +60 to all resistances, and with items like this and the warlock self buff he will reach very high shadow resistance. And warlocks are the best at getting and holding aggro on the magical emperor. Plus they have the most health and are thus easy to heal (even without the soul link; some think that only makes it harder if the healers have to heal the pet too)