I don't know if I want to using that trope. There are going to be some NPCs(And my PCs if there unlucky enough) that are going to think the monsters are angels or demons.
I don't want to revile too much about whats going to happen since you might want to play.
Edite: And here is a Trope you might want to read. http://tvtropes.org/pmwiki/pmwiki.php/Main/PrivateMilitaryContractors