I belive you mean "Isla Margarita."
Been a couple of times.
IMHO, the only really decent diving in Venezuela is in the Los Roques archipelago, which is best done on a live-aboard. It's quite good, but not world-class. Some of the closer islands are a long boat ride from Margarita Island, but can be arranged. Some ops do a night or two live-aboard.
If you are thinking of diving right off Margarita Island, be aware the conditions can be poor (e.g., limited vis), bacterial counts high and op unreliable even unsafe ops (e.g. Octopus). When I go, I just enjoy the good restaurants, discos, casinos and thong bikinis. If you must dive off the island, see if International Dive Center is still operating. Run by the best DM on the island, it's been around a long while. No website or toll free phone. Look it up when you get there. Also ask around about other possibilities.