They are called "Illuminations Cruises." We have not been on one, so I'm not sure what type of boats they are, but I think they ae pontoon boats.
On our last trip to WDW in March, we rented a pontoon boat, like we have every year for the past 8 or so. When we started to drive DD's wheelchair onto the boat like we had other years, the CM told us that WDW had a new safety policy for these types of smaller boats. DD's wheelchair would be allowed on the boat, but she could not sit in it during our ride. He also indicated that if we took the boat from OKW to DD, she wold have to be out of her wheelchair also. Apparently, WDW is worried about their liability if a boat capsizes and someone is strapped to a wheelchair and sinks to the bottom.