I'm fairly confident that virtually all the arms being moved are smuggled, not legally exported, so I'm skeptical that an embargo is going to do much.
https://apnews.com/article/haiti-weapons-gangs-us-trafficking-f06bfb0a7d3b46a1e14ebd7bea95fd71
Increasingly sophisticated weapons are being trafficked into Haiti mainly from the United States and especially from Florida amid worsening lawlessness in the impoverished Caribbean nation, according to a U.N. report released Friday.
“Popular handguns selling for $400-$500 at federally licensed firearms outlets or private gun shows in the U.S. can be resold for as much as $10,000 in Haiti,” the report said. “Higher-powered rifles such as AK47s, AR15s and Galils are typically in higher demand from gangs, commanding correspondingly higher prices.”
That's a pretty potent incentive to smuggle.
When you consider that one of the things that Haitian gangs are smuggling is drugs into the US, I figure that the US is probably already exerting a fair bit of effort to tamp down on smuggling.
https://en.wikipedia.org/wiki/Illegal_drug_trade_in_Haiti
Throughout the late 1980s and into the 1990s, leading members of the Haitian military, intelligence and police were involved in the illegal drug trade in Haiti, assisting Colombian drug traffickers smuggling drugs into the United States.[3] Corruption in Haiti remains extremely high, and suspicions of continued drug-related corruption remain.
So you move a load of drugs into the US, take weapons back to Haiti, make a profit in both directions.
https://edition.cnn.com/2024/05/13/americas/haiti-mss-unodc-guns-drugs-intl-latam/index.html
In a city cut off from the world, guns and drugs keep flowing