I have been to some of the ports you mentioned. Here is a link to handicapped accessible tours in St. Thomas:
http://www.accessvi.com/
I have used a (reg) wheel chair in St. Thomas, St. Maarten, Nassau & San Juan. I'm not sure what you are asking about but here is my observations about these ports.
If you want to tour the islands, St. Thomas is easy access. In Nassau, the side walks are narrow and not well maintained. In San Juan, alot of the sidewalks & streets are cobble stone or brick and it is a bumpy ride! St. Maarten you might find accessible bans.
I would suggest checking on private tours in these ports to see if you can secure accessible transportation. I usually start researching by going to each ports' tourism website. Then, contact different tour opperators and ask about this. If you have any specific questions about the ports I mentioned I have been to, please email me. I'll help if I can.
Karen