Well, besides danger for tourists (don't buy rolexes from strangers on the street corner who wear trenchcoats, etc...), I'll take a stab at your question:
The question of various mexican, carribean, and south american tourist resort destinations comes up frequently. No shortage of tropical destinations down there afterall

And to my knowledge, I've never seen ANY of them where ANYONE has ever been able to come up with some sort of a "no" answer, to casual beach hobbyist stuff. I mean, not the type of "no's" in what you'd envision with some of the European countries rife with cultural heritage problems like Egypt, or Greece, or whatever (with world-class antiquities to protect, etc...)
But some people are still skittish (afterall "you can't be too safe", eh?) and go ask. There was a humorous example where someone, back in the early 1980s, wrote in to the Fisher Co. periodical (they used to have a monthly or quarterly mailer). The periodical used to have a "Questions to the editors" column. People would write in various letters to the editor. In one edition, a reader had submitted a question about Mexico (some beach resort) and wanted to know,
just like you ...if "detecting is permitted there?" Fisher's answer back to this person, was entitled something to the effect of: "When travelling to Mexico, leave the detectors at home". The answer went on to detail dire sounding cultural heritage laws, export laws, salvor laws, etc..
HOWEVER, in the FOLLOWING edition of that periodical, several other readers had written in to take
exception to that answer. Objections like "
since when?" and "
who told you this?" and "
we go down there all the time with no problems", etc... Fisher, in defense of their earlier answer, went on to explain their
source of info. for the answer: THEY ASKED !

They'd simply passed it on to a border lawyer type, or consulate, or Mexican bureaucrat, etc.. I mean, who better to ask, than Mexico themselves, right?

But whomever they'd asked, must've couched their question/answer in terms of treasure salvor laws (wreck diving, etc..) or raiding pyramaids-type things, or exporting gold bars back across the border, etc.. So everything was painted as a "no you can't" type answer, complete with dire sounding consequences.
But the odd thing was, that there is no shortage of md'rs there plying the tourist beaches. There are detector dealers down there in the bigger cities (INCLUDING FISHER DEALERS, doh!).
Thus I suppose it would be no different than if you asked certain archies or bureaucrats here in the USA
"can you metal detect in the USA?", that so too would some likewise say "no". Why? Because perhaps they've got mel fisher's legal hassles in mind. Perhaps they're thinking of federal protected sites, ARPA, and so forth. Yet we ALL know you can still detect, so long as you're not a nuisance snooping around obvious historic sites, and assuming you're not finding the atocha, etc... Thus casual fumble-fingers beach stuff is NOT to be confused with laws regarding the pyramaids, exporting gold bars, etc... But hey, you asked, so sure, someone can give you a technical "dire sounding" answer. Right?
I am no expert on Haitan law, but I'm just saying, that if you decide you wanted to ask someone there, just be prepared, that sometimes you can get odd answers, which don't have any bearing in reality. A possible option is to see if there's any dealers there. Presumably they sell to hobbyist users. Most all the dealers have a listing of their dealers or distributors world-wide, so it wouldn't be hard to do.
But if were me, I'd just go (at safe times of day, of course

)