Don't really see why to give them Animate Dead by another name. It's about the evillest ability on the Warlock list and sure you could refluff it but you'd do better giving them some Celestial Form ability that let them become a celestial temporarily (using the Polymorph subschool introduced in PHBII which means you lose all your normal stuff) or just Summon Monster from a very limited list and a limit on how many monsters they can summon at once.