It seems like a well-meant idea but how do you prevent it becoming exploitative? Exposing dementia patients to random members of the public in a service role with no understanding of the state of their condition seems like a pretty good way of frequently upsetting them. And how does employment by consent work when you can't actually quite remember why you're in a situation and how you got there?

It sounds like - probably to address these concerns - this is a short-lived 'activity' rather than a going concern, potentially with hand-selected and well-briefed guests rather than arbitrary customers off the street.