More Info http://www.cdc.gov/ncidod/dpd/parasites/hookworm/default.htm
Sounds like this can crop up just about anywhere...even in your own backyard. If you want to be safe, you will have to wear shoes all the time.
As I see it unless there is a history of this in Ambergris you are just as safe going barefoot there as anywhere else...
Also moisture in the soil increases chances of getting infected. So it might be seasonal.
I don't know whether or not this includes salt-water moisture...though one of the articles mentions sunbathing on wet sand as a risk.