Normally we don't accept TASes that are just a game-specific replay format, since TASes should be something that can be done in real-time by a superhuman, and just having a replay format doesn't prove that the replay is really possible (for example, the replay format may not prevent invalid key combinations, allow you to input movements and turns faster than the game normally accepts and so on).
A notable exception is that we do accept Doom replays to tasvideos.
http://tasvideos.org/2879M.html I believe this is because they got proven to be identical to sending inputs to the game frame by frame (not 100% sure on this or where it got proven).
So I think that if you can prove source engine replays are identical to what can be done in real-time they can be accepted. (They also need to satisfy some other criteria, like being able to sync on the judge's computer)
(Incidentally, I noticed that
http://tasvideos.org/Platforms.html doesn't list Doom. Should it?)
