I am not aware of any cenotes with the exception of the mainland Blue Hole, I did take a well known cave diver to dive a cave system around the basil jones area a few years ago but that certianly was not a cenote it was just big enough for him to crawl through.
I am sure Protech will eventually comment on this questions also.
Gaz is quite right. We will comment when we have something to say. At present we're in the research stage. But yes, if it's possible and attractive we will offer cave diving (are cenotes just caves in Spanish or are they special types of caves?).