Most of my diving has been in Grand Cayman, which was mentioned in the OP. There are the larger ops (Red Sail, Divetech, etc.) where there will tend to be more people on the boat of different abilities. Then there are lots of smaller ops that provide a far more personal service. I have experience with two of those - InDepth Watersports and Cayman University Divers. Both will have a discussion with you before you get into the water as to your needs, and understand the needs of photographers. If you ask them not to point stuff out for you, but just keep an eye out for you (i.e. be your buddy, if you don't have one) then they will respect that. If you have a buddy with you, more often than not they will allow you to do your thing. (They may not on the first deep dive you do with them, but more than likely will from that point on).
Most divers I have been out with in Cayman are fine - the most recent "bonehead" that I encountered had decades of diving, a camera, and horrible skills - not sure if it was bad buoyancy control, or just a total lack of situational awareness. All his gear was dangling, too, which didn't help. So I hesitate to label any large group as problematic, as it is more about the individual than a group.
The other thing that I love on Grand Cayman when I want to find stuff with the camera is the shore diving. There are quite a few locations where you can get out into the water with your buddy and do whatever you want - if you want to hang out for half an hour getting photos of lettuce leaf slugs, nobody but your buddy is going to be upset.
There are some awesome locations on top of the mini wall there where you can find all manner of things - last dive I was on there I saw a Tigertail Cucumber well over 3 feet long, which was a first for me. Also, at around $13 US a tank, I don't feel so bad just getting in the water and not "sightseeing", but playing with the camera and finding stuff.
So to the OP - not sure if you have already done your Cayman trip, but hope this helps someone!