I can only speak on the basis of a single holiday in St Lucia but there was a wide variety of music around from jazz, cocktail lounge piano, reggae, Belafonte-style (English language) folk and the local strict tempo dance bands called "Kwadrill" (from Quadrille). There's one that played in our hotel called "Shac Shac," which is the local name for the rhythm shaker. The St Lucia CD in the Smithsonian Folkways Music of the Caribbean series (available from Camsco etc) has some examples of Kwadrill bands with the same lineup as the one I heard (fiddle, four string guitar as bass, tenor banjo, drums and shaker). There is a lot of creole French dialect vocal tradition as well (also featured on the CD) but I didn't get to hear any of that.
In the more urbanised areas I suspect reggae is the main music to be heard, except among the older people.
RtS