Well, I'm willing to take Thal's word over National Geographic if it means I can count Bonaire as South American. About 1/5th the cost of the Galapagos.
Walter, I can't remember seeing the Galapagos considered anything other than a "South American" dive, but it has nothing to do with geologic or geographic affiliations... just political in that case. It should be oceanic.
Of course I could go to the Colombian island of Santa Catalina, which is off Central America but it usually listed as a South American dive site!
Good thing I've dived the California mainland as well as Florida (not to mention the Midwestern quarries in my youth)... I guess all my thousands of dives on Catalina really shouldn't count as "North American" continent dives!