Most of the hotel beaches in Cozumel are ricky beaches, like the Florida Keys. The all-inclusive resorts on the southern part of the island would have better snorkling. (Wyndham, Iberostar, etc.) You can also stay in-town and take a snorkel trip by boat. One of the best is Mystic Snorkel. The owner has apartments to rent too. I have stayed there several times (I am a diver). All beaches in Mexico are public beaches. So ,you can go to any hotel and use their beach if it looks inviting.