When I want to learn something, I look for an expert in the field. First, the person has to have the real world experience I'm looking for. I'm not talking about some book learning teacher. I'm looking for someone that has years of experience and would be considered an expert in their field by their peers. Second they have to be good at TEACHING. Some people are good at what they do but couldn't teach it to save their life.
All you want to learn is to make a great vacation video. Check out the trip video the videographers on different live aboards make every week. You should be able to poll people on the board, should be hundreds of them floating around out there. Maybe even ask for an example from the live aboards themselves. Theses are people that do exactly what you are wanting to learn, every week of the year. Once you find an example of the kind of video you would like to do, contact the boat and the videographer and ask what he would recommend you bring on the trip. They might even have stuff on the boat you could rent. It sounds like you couldn't go wrong with a GO PRO and IMOVIE. What better way to learn what you want, practice it for a week and get in some awesome diving.