Well the Voidwoken are a thing, but they are basically voidified (voidformed?) Eternals. Also they COME from the Void, while the servants or rather Sworn don't need to be Eternals, nor originating in the Void itself. Take Windego, she was Sworn alive, not an Eternal at all, a Sourcerer like us and that wasn't any sort of problem for the God King. She still can serve him after her death, after we Slane her (I know it's slain, but meh XD), so if she can be undeadified (now that's a word), why not the main protagonist? I'm pretty sure being a Godwoken wouldn't pose any obstacle, would it? There's no reason it would, or even should.
You know what I meant. God King choses undead as his sworn so they would serve him forever in their unlife. Demons, as succubus, would also fit in this category. Where souls of mortal sworns go after their death we don't know for sure, maybe they go to their respective gods, so undead slaves is 100% foolproof variant.
