Certainly Caribbean FMGs have an uphill battle, but so does every other category of IMGs. Since I'm involved in the process, I can promise you that there's not a list of international schools that PDs keep around and deem exempt from traditional IMG status. All the applications go in the same pile with the other hundreds of IMG applications. The really good PDs are smart enough to read through them, but plenty just discard them.
US Citizen IMG is a double-edged status....while on the one hand, it eliminates visa issues, most people in the states assume there's a reason why someone would study abroad...i.e. they couldn't get into school here, or they were taking some sort of shortcut. Of course, I've met plenty of these from Ireland, England, Pakistan, etc, and they all have some sort of unique reason why the international school was right for them even though they could have "easily gotten into school in the US."
As for DOs, they are often given more consideration than FMGs or IMGs, but they still have a difficult battle ahead, regardless of scores, LORs, and research.
Whether or not the process is fair, it is unlikely to become more DO or IMG-friendly in the near future. So, for those unique snowflakes that have the ability to become US-allopathic students, but are contemplating another approach, they should just go to the US allopathic school, no exceptions.