Certification is only as meaningful as we take it to be. What training do you really need for this sort of thing: none. Especially in the era of online gear sales, the barrier of a LDS requiring someone to show their c-card is now gone. The only real thing left is operators of dive sites, charter boats, and resorts still want to see your card (usually). Even then, someone can still go to a public body of water and just jump in, with or without certification. If you have the money to buy a decent yacht to sail around the Caribbean, chances are you have enough money to buy all the gear you need to jump off said yacht and dive.
If you have the money, it is not hard, certification or not, to buy all the gear you need, including a compressor for the boat to fill all your tanks. If someone in the diving industry is not there standing guard either with equipment sales (but buy it all online, I've never had anyone even ask for my C-card, much less turn down an online sale because they didn't see my C-card) or on a boat or resort, what's going to happen? Since there really aren't scuba police, you can buy all your gear, get your tank filled, and jump in the water with absolutely no training. Is it a good idea? I would say no, but the reality is that the above scenario is not outside the realm of possibility.