You have misunderstood article 28:
It means that prisoners may not be employed by the prison in a role in which they punish other prisoners. Although they can, for example be a referee in a prison football match or work as teachers, provided this is done under supervision.
You can't set up a system in which you give some prisoners the right or duty to punish other prisoners.
The document you linked to has a section on prison work.
- (1) Prison labour must not be of an afflictive nature.
(2) All prisoners under sentence shall be required to work, subject to their physical and mental fitness as determined by the medical officer.
It says that prison labour is a right, not a punishment. Prison labour must not be of a nature that it is part of a punishment.
It says that prisoners should be engaged in work, for which they should be paid. The purpose of this work is to better prepare them for life after prison.
The USA is not fully compliant with this document, In some states, work can be forced and unpaid.
This document is produced by the Office of the High Commisioner on Human Rights, and agreed at the UN congress in 1955. However neither the High Commissioner, nor the UN Congress have the power to decide on the law in the USA, which is a sovereign nation. They can support, assist and advise governments on Human Rights, but they don't have an enforcement division.