Can GM's add users to a game?
I think it's possible, because I've been added to games in the past that I didn't request to join (the games were built after several users indicated interest in the game concept, so it's not like the GM just went and picked some people at random to bring into a game). And I think, back when I first joined RPOL, the friend whose game I came here to join added me, because I certainly don't recall clicking any 'Request Access' links.
Of course, that was long enough ago that my memory can't be trusted for accuracy on that detail...