<sigh> Having had a lot of experience around mentally ill people being in hospital, from a personal and (to a lesser extent) professional perspective, I cannot think of anything more obviously abusive and counterproductive than this idea.
Quite apart from the inappropriateness of sending lay people into a psychiatric unit, whose occupants are very likely to react with "Oh, so I can't get any help for my disorder, but there are resources to push me into a job that I probably won't be able to stick for long". And, having encountered some of the kind of people likely to end up doing this work, I strongly suspect that they'll quite possibly undo any good work that might (ideally, ha!) be being done therapeutically.
If the Government REALLY wanted to do something around mental health and work, the only way to do it is to start by resourcing the MH system properly. Too many people end up in hospital after years of the can being kicked down the road, inept and clumsy handling of patients, and a chronic lack of resources to deal with early interventions. Many of them feel betrayed and let down...so having someone breeze in and briskly suggest they write a CV or something is going to go down like a bucket of cold sick. Which, no doubt, will go down on the paperwork as "uncooperative - withdraw benefits".
I really cannot understand how our governments, of whatever stripe, can be so comprehensively ignorant of what needs to be done to improve mental healthcare, or the benefits doing that would have. I suspect it's largely because it would be a long-term project (plenty of those people in acute units will have had difficulties for YEARS), and they're only interested in Quick Wins.
It's obscene.