THe decision on that matter likely lies with Washington. If the USA are fine with effectively including the Caribbean in NAFTA (Mexico being a member of both would mean that goods will flow freely, nobody has any illusions about the efficacy of its regulatory regime), it will be possible, no matter the political implications. If not, Mexico will have to choose, and given the comparative value of trade and immigration, I doubt it will take CARICOM ver NAFTA.
It would be interesting for the Caribbean in political terms, though. I believe Mexico's population and GDP outweighs not only every single Caribbean state, but all of them combined.
hmmm.. Venezuela has observer status, too. Maybe if Chavez wants to go in and the Mexican government tries to forestall what would effectively be a hostile takeover?