ok, for the sake of this, I'm going to go with the DN.
He is 12th level when he gets this spell, and has an undead Hit Cap of 84(7x12)(Assuming +3 Cha bonus)
Modern necromancers are smart and control a few much stronger undead. In theory he could PAO to get a Skeleton dragon which would dominate with this spell, but we'll be nice and go with a Giant. Undead Mastery give +2HP/HD for animated dead, which stacks with Corpsecrafter for another +2HP/HD and Desecrate for another +2HP/HD.
Cloud Giant is CR 11 and has 17HD
17d12(ave 6)+102=204HP at 12th level, along with a strength of 39 and huge size. A DN who went with being Necropolitan would have 12d12(12+ave 6x11) = 78hp if they weren't necropolitan and had a good con bonus(+2), that'd be 12d6(6+ave 3x11+24)= 63hp
Either way, If they had spell casting in addition to this, it would be madness.
I appologize. I had forgotten about this problem. Carry on, or think of lowering the level even. This spell is limited to just undead so...yeah
However, I will repeat that I love this spell and would probably use it if I can in my next game.