Aaron,
I'm no pilot, so feel free to ignore me. There are plenty of airports around the world without the ILS. St. Maarten has a VOR DME approach, although judging by the approaches i've seen for myself they tend to make visual approaches.
The weather in the Carribean can change quite quickly, good or bad. Theres plenty of airports to divert to if the weather is bad in SXM.
I was under the impression that to be qualified for commercial flight, an airport is required to have and ILS, am I wrong?
Considering how many Commercial airlines operate there, I'd imagine that is wrong.