Nope. He was excommnunicated in 1988 when he ordained four bishops without authority from the Pope.
It is you who don't know the facts of this situation.
You can look them up. There are dozens of threads which detail the facts.
There is nothing that links Mel Gibson's adherence to the SSPX (aside of third hand media info, speculation on the part of the media and the imaginations of some SSPXers). In fact, there was Mass said on the set of "The Passion of the Christ" each day and most of the crew attended. The crew included Jim Caviezel (not an SSPXer) and Jesuits were all over the place (definitely not SSPXers!).