The only thing I know (and this is just personal anecdotal hearsay - so take it only for what it's worth) is that they have taken a LOT of Ross drop outs in the past year. Many of those students left Ross due to some policy changes that were imposed at the last minute affecting their class, which may have prolonged their stay on Dominica. Also (and here's the anecdotal hearsay part), I know personally that many of those students were the weaker students of the class.
What you should look at/really need to know about St. Matt's is their first time pass rate on USMLE Step I. If they are willing to share this information (and it is comparable to the other "reputable" Caribbean schools), then it shouldn't be a problem. St. Matt's moved from Belize to Grand Cayman not that long ago after a history of problems in the former location. So, they do not have a long history at their new location - i.e., it may be hard to judge the quality of the current program until more students fully matriculate, graduate, and move on into the post-grad years (by which, you can get a rough estimate of how they are considered by the programs grads are accepted into).
Long story short, do your homework before you make any final decisions. Personally and from what I've seen, it really doesn't matter where you go in the Caribbean provided you are able to do all of your clinicals in U.S. teaching hospitals. Likewise, a good student first-time pass rate on Step I speaks volumes about the proficiency of the school and how stringent (or lackadaisical, as the case may be) the school is about advancing students who, in reality, actually need remediation.
Good luck in your pursuits.
-Skip
MSIII RUSM