To be clear, there is a place for both volunteers and professionals.
If you want to do it professionally, you are not going to get that much per gig, so you've got to stay fairly close to fully booked in order to survive. Also, there won't be many evening or weekend bookings, it'll be something like one booking around 9:30 or 10 in the morning, one in the after around 2 or 3, weekdays.
You will need to be in place, on time, ready to perform. These places tend to run on schedules, and it takes a lot of effort to get say, 40 people in wheelchairs down to the activity room at 2pm. If you're not there when you should be, it can be a big problem.
Unfortunately, they aren't as reliable as they expect you to be. Events tend to be cancelled and rearranged a lot. I remember in one instance bringing 20 elementary school kids to a facility for a Chinese New Years Art and Music event only to find the facility had been quarantined due to an Influenza outbreak(yes, in nursing homes, at least, they still do that!) There are literally dozens of things that can cause a cancellation(sometimes the AD that booked you left, and the new AD didn't know you were booked) leaving you without a gig, with no time to schedule another.
That said, you can make a living doing this, and, given that it is pretty hard to make a living as a performer, that is a good thing...