No, it is not. Featured games were heavily recommended to test via this, but it is for everyone. If you don’t believe me, why not join the server?
They do public testing, which is what I’ve been testing under. Anyone can submit a game for testing (and the public QA testers would really like to test something). We’re pretty much just waiting for the next game to test, so I definitely recommend people submit their games.
They also do NDA testing, which is restricted to those who have signed NDAs verifying that they cannot say anything about your game while it is in testing. If they do, they can have legal action taken against them.