I haven't been watching Undercover Boss lately but I remember one episode in the first season where the boss sat down with a woman on the phones who was absolutely horrible at dealing with customers. The boss met with her, told her how disappointed he was with her performance and put her on a program/course to improve. The little blurb at the end where they picture everyone and have words up with an update indicated that she'd failed to improve and was fired.
I think that was an appropriate way to do it. It is kind of drama inducing to fire the guy on camera, I think.
But honestly, I don't know how this show works anymore. I know I'd be suspicious if someone showed up at my workplace with cameras in tow, talking about filming a documentary about so and so getting back into the work force/changing careers, etc.