Diving in Mexico doesn't require advanced certification but some things to think about:
Does the resort you're going to offer diving? Some resorts only go a short distance from their shore, but it is convenient.
That stretch of the Riviera Maya, in my opinion didn't have great diving (low visibility, so-so reefs, not much to see, rough water.) Specifically we dove around Playa Paraiso in late October. Dressel Divers picks up from resorts along that stretch and goes to their main shop at the Iberostar. You are bound by their time frame as far as pick up and drop off is concerned. They went out with several DMs/instructors each dive as they usually had various levels of students along. They were a very knowledgeable and friendly op to dive with though.
Dressel as well as other ops will usually set up dives in Cozumel which is worth going to.
I also dove (took a taxi) a few years ago in Puerto Morelos with Dive In Puerto Morelos. There is a protected marine area there and the diving, when I was there (April/May), was pretty good.