Hello! I posted before about my twin DS8, one of whom has cerebral palsy and used his walker for the Pirate Adventure. Every child's needs are unique, so I can only tell you about our experience.
Yes, they were happy to accept our son into the Adventure. Here's a profile of his needs: he used his walker, but can sit safely on the bench seat on the boat; he needed assistance with the transfers from seat to/from walker etc; needed assistance on/off the boat; supervision required on the ramp to board/disembark. I was not with the group, and I don't know if they modified the itinerary given his participation - they did go to all the usual stops, but I don't know if they "hid" the treasure in a more accessible sport, or if DS styaed with a CM while others went on the beach. DS has no social/behavioural/speech needs; he is able to advocate for himself, he knows and can explain his needs and he was also there with his able-bodied brother.
From my pictures, I guess that the boat can accommodate 20 children. There were 3 CM's on board.
I did make a point of being in early communication about potential issues. I confirmed this when we arrived at WDW and we went early to the marina so we could talk more fully with the CMs.
I'm not sure what circumstances the CMs can manage, but I can say that I found them to be very helpful and accepting.
I hope this helps!