The FAR's are not exactly written by scholars for sure.
First thing you have to do is figure out which FAR's apply to the Operation.
If it is a part 91, non-air tour operation, the Rules go awfully vague about floats.
The question becomes who owns the aircraft, is it a lease, charter, privately owned and operated, used in an Air Taxi operation when not being used by the owner, etc.....
When you get all that figured out then you can begin to sort out which rule applies.
I am sure the insurance company will have an interest in all of this.
Keep in mind the FAR's are "Airplane" centric and evolve rather than being written anew thus be careful to remember it must state "aircraft", "helicopter" or "rotorcraft" to apply uniquely to helicopters.
When it specifies "airplane" than it applies only to airplanes.
Commonsense tells one that floats, personal flotation devices, life rafts, and emergency beacon(s) would be reasonable for flights to/from the Islands.....but would they be "required" is altogether different issue.