I have dived several times with one of the people involved in this.
He's paralysed from the waist down, more or less. PADI Divemaster.
He sometimes has problems getting onto and off dive boats, depending
on tides, etc. It would be good if he could get into a lift for exits,
but most boats don't have this. For shore dives, there is a matting
system available that allows a wheelchair into the water. Use a wheel-
chair that is not affected by the saltwater and no problems.

So, the bottom line is - some assistance is required, but a lot less
than the average "temporarily able"[1] person might expect. And once
in the water his SAC is something I could only dream about.

[1] see the Peggy Seeger discography for "Talking Wheelchair Blues"

-Don