I can remember having to fill out paper forms to pass through immigration into SXM. If you were lucky, the airlines would have the forms and you could fill them out during the flight - after you had located your passport, flight number etc.. If the airline ran out of forms, you had to fill them out in immigration. IMHO filling the forms out on-line a few days before your flight would seem to be much easier and more convenient..
If approval is automatic, I don't see any issue.