Nicol Bolas doesn't distinguish between servants and victims.

Slave of Bolas

Gain control of target creature. Untap that creature. It gains haste until end of turn. Sacrifice it at the beginning of the next end step.

The List

Archenemy: Nicol Bolas

Magic Online Promos

Duel Decks: Ajani vs. Nicol Bolas

DCI Promos

If you don’t control the targeted creature when the “at end of turn” ability resolves, it won’t be sacrificed. If it’s still on the battlefield but under another player’s control, the ability won’t try to have you sacrifice it again at the end of the turn after that.

You may target a creature you already control.