On Grand Cayman the cruise dive operator is Don Foster's - they're walking distance from one of the cruise docks. Since they deal with a lot of infrequent divers off the cruise ships, they're likely set up for that. It's not really what I'd call valet diving though - large boats, lots of divers.
Welcome to Don Foster's Dive Cayman Come Dive with Us
We decided against Don Foster's as we want a smaller dive experience.
The snorkeling would likely be better on a snorkel trip. The shallow dive sites off Cayman - except for Stingray City - are going to be 40' deep or so with not much to do on the surface.
The non-diving daughter and I are going on a completely separate catamaran snorkel trip and giving them the space to do their dive day as they want.
For "valet" diving you might check with
Indigo Divers. Not sure of the logistics for getting to them off the cruise - they may pickup nearby. Other small 6-8 pax dive ops often recommended here are Ambassador Divers, Neptunes Divers, Off the Wall and Wall to Wall. The last two book thru the Lobster Pot Dive Centre in Georgetown. The other option for shallow diving/snorkeling in town is the shore dive at Eden Rock.
Cayman Islands - Travel and Tourism Site - Diving has links to all of them.
On Roatan, one option is Barefoot Divers. They run a cruise program and are five minutes by taxi from the cruise port.
Cruise Ship Shore Excursions, Roatan 5 Star PADI Dive Shop
They are booked with Barefoot Divers. Liz and I will have a lazy book and beach day.
