Say if you finish completing the civil war with 100% conjuration and have the Dead Thrall spell. You execute your enemy (General Tullius)

Is it possible to use the spell on someone like General Tullius? I don't know why but I never thought of doing it until now, and his body is long gone and can't be traced.

Is it possible to do this?

I believe so, I have seen vids of people using Ulfric as a thrall.