Tipping in Tromelin Island is probably the last thing on your list of things to worry about. In fact, if you got to the island as a tourist you would have a story to tell! The island is owned by the French and is an overseas territory. It is a protected island due to its fauna and wildlife. You won’t be able to visit unless you work for the government or wildlife protection.
If you do get the opportunity to go the tipping wouldn’t be a concern! There isn’t any services on the island and it is uninhabited. Have fun though! Its a once in a life time experience!