Years ago I did it. Not sure if it is the same company or experience, but I had no concerns. There were certainly restrooms and so a changing area. Don't remember if there were lockers.
Not sure how much stuff you are considering taking, but I would only take what you expect you use. I'm sure I didn't change and just wore my swim shorts and tshirt.
Some pictures from years ago:
Montego Bay - Conquest - Jungle River Tubing - Nov 2003