Necropolis vs. Stronghold

Finally!!! Today, Sёnya defeated that guy four times in a row))) Twice with a Stronghold, once with a Dungeon, and once with a Castle, all destroyed by Galthron. By the way, why don't Blindness and Curse work on Necropolis units?
p.s. please, can you tell me what else doesn't work on the undead?
p.s.s. sorry for the off-topic, but does anyone know if you dig up the Grail and then, to prevent it from being taken to the city, just attack someone (a neutral or enemy hero) and then run away and buy the hero in the city, will he have the Grail?