Are military personnel required (or allowed) to salute while they are military prisoners?
It would depend on the type of military prisioners you’re talking about. With regards to POW’s, the accepted custom has been for military POW’s to salute the commanding officer of their facility when addressing him properly, but obeying the guards and lesser officers of the facility wihtout salutes when not making formal requests. Prisioners held on criminal charges are not permitted to saluate or be saluted.