I think this would not be called "being paid for doing HR's job". It's typical that union reps from the employees are still employed 100%, but get leave to handle union business (or worker's council business) for a certain percentage of their time ("freigestellt" in German, but I cannot find an equivalent, maybe "released for", but this sounds fishy to my ears).
Their work contract (at least in DE) don't change which avoids part of the dependency problem.
@TimWardCam @doctormo
Also note that commercial enterprises and organisations on the government / local admin side are typically rather different beasts. At least in Germany the laws also partly differ.