I saw the warnings in the Disney brochure, but never saw any nudity in St. Martin.
My first cruise, way back when I was 23, was a different story. It was on the Mermoz, run the the French cruise line Paquet. 98% of the passengers were from France, and there were topless sunbathers by the pools ON THE SHIP.
Out of the 450 or so passengers on board, only about 25 were not French, and there were only about 4 kids on board.