I'm currently working at a rehab facility. It also has assisted living, long term care, and hospice. The facility allows churches to sign up for planned activities. The witnesses hold a service once a week at the long term care facility. These patients are mostly dementia, and will never leave the facility with exceptions for doctor visits. They also will not remember any discussions for the most part. In addition protections are in place to safeguard their finances from the witnesses or other exploiters.
A good portion of these patients are very old with no visiting friends or relatives. There usually is a 1:8 ratio of nursing aide to patient. These are patients that are total care, they can't even feed themselves. So basically the witnesses provide a little bit of companionship for these patients, and in return the witnesses can log field service hours and I guess a shit load of bible studies.