We often (twice in the past 3-4 months) sent desirable prospective hires for coffee with a current employee to allay some of their fears. Both accepted jobs shortly after this, and likey would not have if we didn't give them relatively "unfettered" access to the real deal.

Sometimes sending the interviewee to lunch with potential co-workers is an optional part of the interview. I've been on many such lunches (mostly as a potential co-worker, only once as an interviewee)

Obviously, it's up to management if they want this to be a part of the interview.

definitely is but I've found that if the manager wants the hire (esp post the company deciding to move forward with an offer), then you have leverage and this is a very sane ask.

you tell the hiring manager that you want to do that and make it part of the hire. If you're in town you do it a separate day.