Honestly if anything I think it would be easier than vetting someone with no background, you already have what they've been convicted of. Idk how many burglars or murderers like to dabble in arson.
If only there were more context and nuance available than "convict/not convict" when making such determinations and risk assessments about candidates...
In my job, I occasionally facilitate training for prisoner firefighters. Not only do they all love the job, they are also the best FD we train with. They read the material, study procedures, get it right when being observed. They get to stay at the firehouse instead of the prison itself, so both getting invited to do it and continuing to do it are huge for the inmates. They also love it. It burns my biscuit right up that they'll not be able to be a firefighter when they get out.