We only did a cruise in Tahiti on Princess, but based on my reading beforehand, technically Tahiti is pretty topless friendly but as far as straight c/o, not so much. And there is no way to make a blanket statement about 'over water bungalows', you would have to consult the particular resort you are staying in. Depending on the resort, the individual bungalows could be very private from each other, but the pictures of most resorts I have seen is that they are all lined up right next to each other. The traditional wisdom that I have always heard regarding nudity in Tahiti is that you can get someone to take you to a deserted motu and you can be nude there.
If you decide to go, Tahiti is fabulously beautiful. Enjoy..
We found that a strategically placed towel on the railing gave us enough privacy to enjoy nude sunbathing on the deck of the over water bungalows. They generally are far enough apart to make it comfortable.
Complete nudity is not legal in Tahiti. We had too much rain during our 6 days there last month to really see many people on the beach or on overwater bungalows. I found the platforms to be pretty open. Not many people walked by, but enough so that nudity there would not be feasible. I suppose after the sun goes down you can do what ever you want. Next year we go back to St Martin.