[Baalz]

Vampire lords (and LA Ulm counts) have blood magic, so they can sabbath slave. Assuming you have some other astral/blood mages you can uber buff them - have a couple communion masters cast invulnerability, fire shield, phonix pyre, soul vortex, breath of winter, hell power, etc. etc. Use cleverly timed reinvigoration to keep from overfatiguing them with off path spells, and use the communion boost to cast whatever nasty battlefield enchantment you have available (wrathful skies, foul vapors, grip of winter etc.) Have the masters withdraw and the slaves attack. You get pretty ridiculous immortal kamikaze killing machines with a good chance of wiping out entire armies and little chance of any losses on your side.

Oh, regular vampires - which you'll have for free from your vampire lords are great in this situation to cause a distraction while your communion goes off - who cares if they die in droves? Best to berzerk your Vampire Lords though, don't want them routing because the chaff dies.