Hmm, definitely an interesting start. For some reason, I can't shake the impression that "Brother Zed" is a well- and fully-hidden Harry Potter, come back to clean up the last traces and loose ends. Methinks Severus should tread most carefully around him and the school in general.
I can understand why Harry would need another identity and this one is so unlike him that few would suspect. The final battle obviously didn't go the way Tom expected, there is something to the old admonition to "let sleeping dragons lie", but I doubt he'd have believed it possible.