If he's a true mobster, he'd know his way around prison regardless. Since you brought up Oz, look at characters like Stanislofsky or Jia Kenmin who don't have a crew to back them, but don't have to worry about getting raped or killed on a daily bases. Compare that to guys like Beecher or Guenzel who were targeted the second they came to Oz. The inmates can sense the weak prisoners and almost always go after them.