It would seem to me that if you were in an "exotic" location, you might have very little recourse outside of notifying the owner/management. In these types of situations it almost always boils down to your word against theirs, and since you are no longer there and registering your concerns, the chances are that very little, if anything, will be done about it.
I captained a liveaboard that spent time in the Bahamas and Belize and because it was a US flagged vessel, drug use was grounds for immediate termination, and the company had a zero tolerance policy for drugs on board (this could be a very serious offense-if the USCG finds drugs on a U.S. flagged vessel, they have the right to confiscate the vessel).
I did encounter a few guests who were smoking pot on the sundeck, but after explaining the company policy and the risks of having the vessel seized, they were always very cooperative and apologetic.