I'm willing to assume the OP is a concerned family member, that doesn't really understand the situation and is worried his brother is making a big mistake.
The answer to your question is "Maybe, but it's a big uphill climb and a good number of people don't make it".
SJSM is a medical school, and awards an MD. In order to be successful, your brother would need to:
1. Complete the first two years of medical school, which are mostly about learning science -- physiology, anatomy, pathology etc. Mostly book learning.
2. Take the USMLE Step 1, a national exam that anyone willing to train in the US needs to take. He needs to get a good score on it to be competitive -- just "passing" could be a problem.
3. Complete 2 years of clinical training, doing rotations in US hospitals
4. Take the USMLE Step 2 CK and CS. The CK is a multiple choice exam testing clinical knowledge. Again, he needs to do well to be successful. The CS is a "fake patient" exam, it's pass/fail only. He needs to pass it on his first try.
Assuming he does all of that, he would then apply for residency positions in the US. His options for fields might be limited -- the least competitive fields are Family Medicine, Psychiatry, and Pathology -- although that could change over time. Many mid-competitive fields like IM and Anesthesia are obtainable. High-competitive fields like General surgery are very difficult. Ultra-competitive fields such as Dermatology and Orthopedic surgery are near impossible.
The problem is that there are multiple places he could end up in trouble:
A. His preclinical coursework, or Step 1. Chances are he did not get into the Big 4 or a US school because his GPA and/or MCAT wasn't good enough. Although these are not perfect, they do tend to predict who will do well in med school and who will not. The rate of learning in med school is very high -- much higher than most colleges. The support services in the carib schools tends to be weak. He could easily start failing courses, or not do well on the USMLE. He really gets only one try at the USMLE -- if he fails, he's in big trouble (although he can take it again to pass, once you fail your chances of getting a spot are more limited). If he passes and does poorly, you can't take it again.
B. Clinical rotations. Many of the less-well-known carib schools send their students to less ideal places. How good are SJSM rotations? I have no idea. But they could be terrible. And they could be unstable -- hospitals that currently let SJSM students rotate there could change their minds tomorrow. Some schools literally make students set up their own rotations. Some hospitals charge for this -- that would be on top of tuition.
C. Step 2 CK and CS -- same deal as before.
Any problems along the way, and he'll end up high and dry. If he gets a foreign MD and can't get a residency, there is NOTHING he can do with the degree. It will be worthless.
Now, let's say he does all of this and beats the odds. None of the carb schools are open about how many people fail out, and some try to string people along to collect as much tuition as possible. But let's assume all goes well, he scores well on the USMLE, does well on his rotations, gets good letters, and applies for a position. If you look here:
http://www.nrmp.org/wp-content/uplo...s-in-the-Match-IMG_Final_Revised.PDF-File.pdf on Chart 15, it breaks the match down by country. They don't break it down by school. SJSM is on three different islands, and none of them are listed. But you can still see what happens. SGU is on Granada, and the match rate looks to be about 2/3 or so. Ross is on dominica, with a match rate of 50%. AUC on St Martin, match of 60+%. But look at the other little islands. It's pretty bad. And if he's not a US citizen, it's horrible.
So that's the scoop. Statistically, this is a terrible idea. Sure, it's possible that he could do fine and get a spot. Some people from SJSM will get a residency program. But many will end up in a mess. Is your brother going to be a top performer and be successful? Maybe -- but if so he should have taken the MCAT, scored high enough on it, and gotten into SGU/Ross/AUC where his chances would be much better. And there's some concern that things will get worse -- more US schools have opened and established schools have increased their class size. This MAY put a squeeze on smaller carib schools (it's complicated, there are entire threads about that topic!)
If you haven't read it, look at this thread and the blog linked in it:
http://forums.studentdoctor.net/threads/now-a-cautionary-tale.1107726/ He went to a non-big-4 carib school, and see how it worked out for him. This is what we are trying to warn you of.