It's possible, with all that time and isolation, for anything to morph into just another criminal enterprise. I've seen religious groups serve as nothing more than a thinly veiled gang, and I've seen religious groups take a deeply spiritual and genuine approach to their faiths. And of course everything in between.
When you consider what really landed most of those folks in prison; addictive personality, inability to cope with society's norms, and quite often some serious psychological problems, it's no wonder you see some extremism. Some times the change they experience in the joint is positive, some times not so much. Prison is not a normal kind of place by any measure.
Oh, and I have a friend who did time in the federal corrections system for a variety of crimes and he told me one man changed his life in a way he never anticipated. He went to an Easter service as a way to break the monotony and heard what he considered to be the sermon of a lifetime. The sermon was delivered by a fellow inmate. Anyone remember Jim Baker? Seems once the money and fame were stripped away he became extremely effective. My friend is still a bit of a bucket head but has managed to stay out of jail. He gives the words Baker spoke that morning much of the credit for his change.