Thought I would respond to this one...
My son was in a wheelchair, so I am very aware of the non-accessibility in San Pedro.
Caribe Island is not accessible, although we have hosted some disabled guests. Sunbreeze is the only place I am aware of that is accessible, and there are pitfalls even then.
Getting to and from the airport in Belize City could be an issue too. When I had a cast on my leg, they drove me to the plane on the golf cart, then picked me up and put me in the plane. It's not easy, nor comfortable.... but it is doable...
As a member of the Chamber of Commerce in San Pedro, I have brought up the subject of accessibility, but it's just a small issue in a big ocean.