In any case, ssh public keys are self-created and are not validated by
TTPs. So, the very first time you connect to the server I don't think
you would be able to detect a mitm attack.
unless you knew the key's fingerprint. Otherwise, no, you wouldn't detect it. Until the next time you connected through tor, and you got the real key 8) Ironically you'd think the real was the fake, I guess.