Any time I shopped (a few times a week) there were 3-5 workers from the assisted living home nearby. They were all VERY nice but a few of them accomplished almost nothing - those workers were paired with someone else who did 95+% of the task (shelving, bagging, etc).
I talked with many of them often - some really liked talking and I was happy to chat as long as they wanted. I met the driver/supervisor from the home - I wanted to know if I was talking with them too much and keeping them from work and he wanted to know if they were bugging me ("no" in both cases). He told me this was the highlight of their life and it was great that the store hired them. It gave them a job and paycheck and made them feel normal even though the paycheck wasn't much.
I don't know if the store was paying under minimum wage. But they were not getting their money's worth whatever they paid (I knew many teens and retirees who wanted those jobs and would be able to do more). The store really was not getting ANYTHING from 2 of the workers. But the workers were getting a lot of satisfaction (according to the supervisor from the home) and people like me got a lot by interacting with disabled people more than I ever had.
I don't know where the line is. Some companies will abuse any police/rule/law. But there certainly are cases where paying a disabled working less than minimum wage is a good thing for the worker. For every company that abuses these rules, there are companies who will opt to hire an able-bodied worker over a disabled worker if they have to pay minimum wage. I'd prefer to error on the side of the line that allows those who really aren't able to do much to still have a job.