I do not know Keating personally but some friends do and think highly of Keating. The weakest part of Keating and his associates is on this personal evaluation of others stuff. Doctrinally, Keating seems fine but, absent something specific from Mel Gibson himself one way or the other, we ought to reserve judgment. What someone heard someone on the radio say as to what a friend of that someone heard from Gibson does not suffice.
Right now, Gibson is too hot and has too many controversies concocted by others swirling around him for the world (i.e. us) to dispassionately discern the specifics of his faith.
If Mel says he is SSPX or that he is sedevacantist or that he is a traditional Catholic in communion with the Holy See, I am willing to take his word and his alone for what he actually believes. If he chooses to keep that information to himself, that is OK too. There are too many people grinding too many axes (not you) trying to lay claim to him or to cause others to reject him for whatever reasons.
Mel Gibson may or may not be a sedevacantist, I don't know for sure. However, I would not believe anything coming from Catholic Answers. These are the same people who make a hobby out of slandering other traditional Catholics like Gerry Matatics by throwing around accusations of "anti-semitism." Kind of reminds you of Abe Foxman, doesn't it?