Is Aruba The Only Island That's Out Of The Hurricane Belt??
 

Considering taking a trip to the Carribean in September.

Aruba, Bonaire, and Curacao

grenada is another good option

There aren't any islands which are immune, but some are very low risk.
This link shows you the detailed data:

http://www.stormcarib.com/climatology/freq.htm

I'd also point out that I suspect that data recorded prior to the 1970's was probably sketchy in many of the poorer countries.
I think it's difficult to imagine how the Dominican Republic can suffer 4 category 4-5 hurricanes while parts of Haiti have had none. Could happen, I suppose, but most likely it's just bad data.
That is, there's probably a lot of underreporting.