I don't think the idea of parole makes sense, since he told the DEA when he was being interrogated that he has a permit to carry a gun in multiple states (when asked which ones, he said it would be easier to list the states where he did not hold a permit). He is also a licensed PI in NM and all of the other states where Los Pollos Hermanos operates (which was most of the Southwest). This would not be possible if he were a convicted felon, or even if he had an aggravated history of misdemeanor-level crimes. As far as we know he has never actually been convicted of a crime, and it appears he has not, since if he had, Hank and Gomez would have known it when they were investigating him. We just know that his tenure as a Philadelphia police officer "ended badly," whatever that means. I also don't know that a convicted felon would be allowed to work in such close proximity to the courthouse.
It seems to me his working as a parking attendant is either a function of that being the only job he could get in the ABQ area, where his granddaughter and daughter live, after leaving Philadelphia, or some kind of undercover operation on behalf of a criminal heavy. Working as a parking attendant at the courthouse would certainly give him the ability to monitor the comings and goings of prosecutors, judges, jurors and criminal defendants, and that information might be valuable to someone inclined to do them harm, kidnap them, or otherwise mess with them.