Like I said a while ago, I think that those guys from the intro don't all represent in-game characters 1:1. We can still argue about Ghirahim being in that intro shot, but IMO assuming that Demise=middle guy is a very far stretch which takes a lot of imagination.
I've finished my first playthrough of the game just yesterday (not 100% though), and I can definitely confirm that
besides Demise, Ghirahim and maybe Batreaux, there are no other demons in the game (I don't know if Batreaux was part of that same tribe or not, I only found 50 crystals for him and so I didn't make him human - maybe he tells you more about his origins if you finish his sidequest)
