I'm not sure what Shipwrecked book you mean....did you mean to say Stormwrack? If so, then yes, that's an acceptable source. In fact, I'd say a great deal of the material in that book is quite appropriate for the setting of this game.
As for UA variant rules, I'll consider anything, but I reserve the right of veto power.
Also, a character of an aquatic race will certainly require a very strong background to explain why such a character would join a (nonaquatic) adventuring party. Having said that, I'd be happy to consider your character concept. I'll let you know if I think it needs tweaking.