My disabled ds uses this type of clubs/activities, his are non-residential and yes, they do have volunteers helping.
There is usually a paid employed staff who run the place and the volunteers fill in various roles depending on interest, eg sports, crafts, music/singing etc.
The residential place I know they operate approx 9-4, they do gardening, crafts etc.
It's hard to generalise as every disabled adult is so different but they usually work in small groups. Patience is definitely required but it's not a very stressful/pressured environment as far as I can see.
I was involved for a few years in one of the groups running 1-2 outings/activities p/year, some were on a rota basis.
You could enquire and find out what particular activities they are looking for volunteers for, I had a friend who went in for one morning p/week and they were making greeting cards and similar paper crafts.
I do know a number of people who run the groups, both staff and volunteers as I see them a few times p/week, if u have any specific questions I can ask.