Just to clarify, nobody is entirely reliant on a guide dog. A guide dog is a tool that assists someone in certain situations, there's loads of tools blind people can use to navigate, they may have a preference but the prison systems don't really care much.
In sentencing, disability can often be used to get a judge to look at a non-custodial sentence, or custodial in an alternative environment, it can even be a mitigating factor to get a lesser sentence.
But if they do get put in there, then it depends so much on the system. In some countries they will treat you very well, in others you'll not survive long.