My last cruise was NCL Getaway stopping in Roatan, Belize, Costa Maya, and Cozumel.
In Roatan, used ship excursion (due to timing) they use Anthony's key Resort.
Belize , NCL doesn't do any dive excursion in Belize City anymore. Also heard that the next trip after ours, NCL will be pulling into it's private island Harvest Caye. I doubt any dive excursion there or any chance to book privately.
Costa Mays used Doctor Dive (or is it Dive Doctor?) Nice operation. got some nice dives although visibility was not optimal (only about 40 or 50 foot)
Cozumel used Aldora. Had a new DM and new diver with a full face mask (I think her name was Dyson Hoover). the DM called the dive when she ran low on air, it was the shortest dive I ever did with Aldora, I came up with almost a half a tank. This was quite a contrast to the DM we had in March who just took the heavy breather to the surface got them on the boat, and came back and continued the dive.