Really loving undead warband, very cool classes and beautiful synergy between hero abilities.
There are however a couple things I would change:
1- The Dreg ability "Humble Servant" should be based on a % rather than a fixed amount: pay X% HP and heal the vampire for 60% of the total HP sacrificed
2- The Ghoul should have some kind of perk to make up for the total lack of armor (I don't find buffing the weakest Necromancer spell a particularly useful ability). I would go for a buff in speed and a poison effect on hit; presently I don't see any real reason to pick Ghouls. If I need an expendable meat shield that can dish out some damage before going down I'll go with the Zombie PERIOD; yeah they are slow but they are completely immune to psychology and poison, they don't impact warband morale when they get knocked out of action and are immune to most permanent injuries... ok they are more likely to die but honestly... who cares if a stupid Zombie dies?
3- To compensate for the Ghoul buff I'd rebalance the Zombie's physical stats (16 strength is too high) lower max weapon skill and completely take away any off-hand usage, severely limiting its fighting capabilities, and instead give it higher base HPs, a natural damage soak ability (like that necrotic flesh damage resistance that keeps a zombie going until basically dismembered ) and make them cause fear. this way we could differentiate the roles of the 2 undead henchmen classes: a fast but very frail DPS with decent fighting skills and a revolting, slow, putrid meat-sack good only to use as enemy punching-bag and vampire mobile cover
Anyway really good job on this one! The undead have immediately become my favorite warband in the game
Now I'm waiting for you guys to give us more customization options... WAAAAAY more