As a side note, aside from Mound Fiends (D3/U3 for 28 death gems, Conj 7 IIRC), there's at least an ice devil with unholy.
U3 is enough to raise either longdead or ghouls; the latter might be handy for supply-free siege defense, while the former are supply-free amphibious troopers with some gear. If you reach U4 (possible through the Sword of Injustice, and Last I checked a Ring of Wizardry also boosted unholy), you can reanimate longdead cavalry; could be useful if you can't be bothered to pay the gems to summon them.
But yeah, you don't get to cast Apostasy unless you're Broken Empire Ermor.
