Interesting, Death's Eternal Embrace reminds me of the ability the Archdemon had in DA:O. It does, however, seem a bit overpowering, especially if you allow an NPC to take it. Destroying all of a character's controlled undead, especially if they hide them, is going to be for all practical purposes- impossible.

Perhaps a loophole or specific weakness should be put in to prevent that kind of abuse (LIKE in DA:O).

Blackened Rage says add charisma score to maximum hp. Is this intentional?

Why only mindless undead- these would be completely useless regardless of what bonuses you gave them at epic levels.