So, i played as Necromancer and wanted to revive a Guardian Angel. When doing that, you are kind of wanting to control somebody that can still do something, as the Guardian Angel can still defend its target when dead.
When i did use the Guardian Angel on me, he didnt protect me.
So i suggest that you wouldn't be able to reanimate a Guardian Angel because it doesn't do what you actually want, or you could somehow actually make the Guardian Angel protect the Necromancer's target.