Oh, no, I wouldn't say that his Name is John Marcone, but I don't think he could have kept all of himself in his birth name, either, and still made John Marcone as real as he is, you know? The Baron isn't all he is, but the Baron is more than just a facade or shadow, too, like Lash was more than just a mask for Lasciel, and it's all tied up in the giving and taking of names.

So anyone trying to bind him with John Marcone would find themselves in a mass of trouble because they'd have left out most of what he is, but the thing is, I think anyone trying to bind him with his birth name would find John Marcone the mafia lord still free to come down on them, because vanilla mortals' names are tricksy like that.