It's fine! Technically, at least canon-wise (Vampire Knight), Zero is hyper-sensitive to whether someone is a vampire (which actually don't follow much of vampire lore; they're very much alive, aren't affected by religious items/garlic, can eat normal food, etc) or human, or even another hunter (they contain very light traces of vampire DNA). For the game, I've mostly been playing that he can pick up on any differences from the typical human being. So, at best, I'd say he would be able to tell that there's something different about Tony, but unable to pinpoint exactly what it happens to be.

Also, feel free to ask whatever else! I'd be more than happy to give a little insight, esp as Zero is a bit of a special snowflake in his canon. Alternatively, he has a permissions post. :)