Have seen free divers north of cut - one almost got run over because he was in the "boat road" this means that boats travel out of San Pedro Town North & South along specific routes, I believe it is illegal but definitely unsafe to be in these boat waters especially if you are not familiar with area. Many boats are going very fast along these routes.
Most kayakers snorkel not dive. The tourist kayaks might not even hold all your gear safely.
IMO not safe to kayak & dive - if there is a medical emergency you are on your own miles from help.
Possible trouble with sharks if chum, fishing bait or fish parts get dumped overboard by passing boats.
Also milk jug of air marker is barely visible when boats are at high speeds - let alone human heads!
If you hire a guide you can take private dives when & where you like. We used to fish until hot, then snorkel, fish or shell some more then have delicious shore lunch and fish & snorkel back!
Check out Marty's map page on this website for dive sites up north http://ambergriscaye.com/maps/index.html
Three of my favorite Mexico Rocks, Tres Cocos and the San Pedro Channel in town, this cut is deep and used to have a ship wreck, it is where we saw sea turtles swimming in & out through the reef.