Rolando, our penal system works a bit different than this in the states. Obviously, it´s in the nature of things that a prison is build to limit the personal freedom. This is what both have in common. You will find here also bars on the windows.

Responsible for the limitations of freedom can only be the state, the conclusion is that every CO is a civil servant/state official. They work for the justice department of the federal country the prison is in. No private company could do this, it´s forbidden by constitution. It means when a private company became allowed to take over some tasks in a prison then it doesn´t mean that their employees would have the same rights like the COs.
The main goals of our penal system is on one hand the limitation of freedom for an inmate and on the other hand the re-integration (in principle starts it on the first day). What no CO is allowed to do is to harm is the human life and dignity of an inmate in normal prison allday. The COs are obviously allowed to defend themselves if needed. But pictures like those i have seen in Lockdown or Lock Up are not imaginable here when heavily armed COs tried to recover the control over a prison (i guess it´s not the usual prison allday). A neighbour of me was for more than 5 years in a prison, he told me it was like in a pathfinder camp. I have no doubt he told the truth.
German inmates become often the possibility to work. And they earn obviously some money. Not much but i guess an american inmate would dream about. Work is part of the philosophy of our penal system, work simply decreases the violence readiness and when the inmates work for a better future or to have a more comfortable life in prison, why not ? When prisoners work for a company, i´m sure the company has to pay usual wages like in the free world. The justice department observes this. I´m not sure how much money the inmates get from their wage, i think it´s only a part. Psychological help is afaik offered in every prison to learn the inmates to have a future life without new offenses. Obviously do i not know the whole allday of a german prison, but that inmates are treated like animals or scumbags by prison staff, this would i exclude. The inmate has too much rights to fight against.