Hard disk cameras often seems to have compability issues from what I understand. And the footage is more compressed than what you get using HDV and MiniDV tapes. (1h HDV takes up 13GB hard disk space)
Same goes for DVDs.
You have cameras coming out that records to Compact Flash (Sony and Canon) that are very good.
The great thing about shooting HDV on MininDV tapes is that they are cheap and you have sorted out the storeage problem straight away.
The downside is capture time. It´s real time.
Using cards allows for faster capture times, but you have to buy disk space or burn DVDs for storage.
(I´m capturing 3h footage from today as I write, it´s a pain to have to wait an hour, then change tape. It´s getting late over here)
For a small, cheapish HDV (that records to tape) camera I recommend the Canon HV20. I have this camera as a B-camera for my Canon XL-H1. Great images.
BUT, it might be easier to find underwater housing for Sony cameras. You should look into that as well.