Yeah, he would be too obvious, but I can't get past that comment about the 3 confirmed dead. I would hope that wasn't just a crappy editing issue.
Unless there's some obscure background character, yes, they're the only ones to appear in each season. Hell, as far as I can remember, Jack, Aaron Pierce, Tony, Kim, and Mike Novick are the only people who have had key roles and have survived since day one.