Why not? Other expensive things are granted (lobster tail, steak, etc...) why not these items? If guards make sure that the prisoner finishes all of it, it cannot be spread through the prison.
If so, what are the restrictions, if any?
It's just at the moment i am on Google Earth, and out of curiosity i typed in the name of a place where a relative spent some time in prison.
and it has an aerial view of the whole prison, exits, main entrances, basically a map of the prison grounds...