I saw sample menus on their website, are there choices for dinner that aren't fish/seafood?
Yes, they're very accommodating, they want you to be happy and enjoy the food, the island, the whole thing. They have a system that works really well; in the am at breakfast they show you the menu for the evening. If there is anything on it that you don't care for you can substitute from the lunch menu (which is good and has quite a variety) or modify the dish (like no sauce or whatever). In general there is a really good variety of food on the menu from night to night.
Get an answer from Vahine Island - Private Island Resort & Spa staff and past guests.