This:

“The guests’ jokes were often aimed at the shelter’s more privileged volunteers and employees and were what many people might consider crude or offensive…”

and this:

“ The jokes, which the consumers often made at the expense of service providers…”

…are not okay. I taught high school for over twenty years so I developed a hide like a rhinocerous when it comes to getting crap from other people and not letting it effect the way I treat them, or my self esteem. But no institution should allow anyone to be subjected to derision as a regular condition of their employment or volunteering. No one is so sick or so poor that crudely insulting others is acceptable behavior, unless the butt of their jokes specifically says it is. Being mentally or emotionally ill is not a license to be an asshole. I saw some fine young teachers driven out of education because they couldn’t put up with this sort of thing from their students. If you want people who are sensitive to work with the mentally ill, this is not the way to do it.