I have so strongly disagree with this idea. If you get banned it is for the reason that you are incapable of following the rules. The server rules still apply when you are an inmate. What stops someone from breaking the rules when they are put in prison? Absolutely nothing. Besides, prison is a sense of In-Character punishment for violating In-Character laws, while disciplinary actions taken against you by an administrator is Out-of-Character.
I understand that prison roleplay can be boring if there's a lack of inmates. If someone who is supposed to be banned for violating the server rules is instead imprisoned, then they would most likely start breaking the rules of roleplay and the server while in prison. There is no sense of risk of you being removed from the server if worst case scenario is that you are put in prison instead.
I can agree with one thing though, and that is that there should be a sense of punishment in regards to your character if you are caught committing a certain server violation. Let's say that you continously evade the cops and the reason for you evading the cops to begin with is that you are reckless driving continously, you bait the police into chasing you and so on, then I agree that the administration should be allowed to remove your vehicles, and that you would have to grind money to be able to obtain them again. But again, that is simply to prevent people from being completely mindless in traffic to the extent where they don't care about the server rules.