You are basically just repeating what he said, but it doesn't answer my question. After all I'm not ssh-ing to GitHub directly, I'd use git, which will use ssh as a transport, and I don't know if git will use the subdomains I provide the way I think it should (my primary concern being to prevent GitHub from displaying 2 public keys for a single account, so that 3rd party cannot tell that it's most probably the same person).

Of course, I can test it myself, but since somebody already does that I assumed I could just ask.