I have always worked with people with learning disabilities and physical disabilities, and it is fantastic when individuals with disabilities achieve something that the rest of us take for granted. Having said that, I appreciate your concerns, if the hike is not well-planned, etc.
Capability Scotland have successfully led teams of disabled walkers, including wheelchair users, up and down Ben Nevis a couple of times now, and I'm pleased to see they are repeating the fund-raising challenge again this year...
http://www.capability-scotland.org.uk/news-events/events/ben-nevis-challenge-2013/I suggest the individuals you are concerned about either link in with Capability Scotland and do the hike with them in August, or contact them for advise.