Jackieo, I don't think there is any problem wearing a thong. To be honest with you, the only people I saw usually wearing a bathing suit were the tourists. Usually the locals wore their shorts and shirts in the water. I did find that people don't walk around in just their suits like they do at other beaches I have been too. The first day I was there, Karin and I walked through town in just our bikinis, but felt a little odd as noone else was, so we went into a shop and bought a short sarong to wear when in town. I am use to the beach towns here, where you wear your bathing suit everywhere, ride your bikes in them, and only put on a pair of shorts or a cover up when going into a nice restaurant on the beach.
You will love Seven Seas. Everyone there was so wonderful and the rooms were the perfect amount of comfort. Not too fancy that you forgot you were on an island, but not so rustic that you hoped you were so drunk you would pass out and not notice where you were sleeping. Have a great trip.
Punta Rebel Girl