I don't know who the cruise operator is - Foster's does most of them but they don't list NCL.
I suspect the DSD is done off the closest dive site to the shop(s) - which for all is off their dock. All are walkable from the cruise tender dock. Cheeseburger Reef - which I assume is the site for most of them since they're on it is a known dive site. So is the wreck of Cali which is not as intact as it sounds like so safe for DSD's.
Options in Georgetown who offer cruise dive programs.
Don Foster's Dive Grand Cayman
https://www.diversdown.net/Discover_Scuba_Dive.html
Cruise Ship Visitors to Grand Cayman | - there's 3 operators there -
Wall to Wall,
Deep Blue Divers or
Off the Wall.
Eden Rock is 500' from the cruise dock. It or the Grotto aren't much over 40'. Note that the silversides
won't be there in March.
http://www.edenrockdive.com/
Fosters's is sort of on the south end of the Grotto also.
There is a process to build a cruise pier on Grand Cayman that was approved last month. So if that has started by the time you're there - Eden Rock is going to be buried under the pier. So they'll be dredging in that area initially. You might try the shops north if that's the case - Lobster Pot or Diver's Down.