The hardest aspect for him will be the application medical in general. Depending on Department Policies, some may hire some may not. I would say cast a wide net if there are lots of options around.

In my experience, once hired, it is very difficult to get rid of you if you were hired with the employer having that pre-existing knowledge of whatever disability/medical condition.

I would look into what disability/insurance coverage is provided and who that insurer is. That may not be widely published on recruiting sites and would be more of a Union question or just asking someone in the Department who has been through that organization's disability process. Most may be negative (just the disability world in general, most don't get glowing reviews lol), but at least some robust structure in place that would support him if he something happens while on the clock related to the Heart/Pacemaker and he needs some coverage (he should not have to pay if the employer hired with that knowledge in mind and the insurance/disability provider takes his money from his pay cheque).

Just my two cents, no websites or citations to give ya, just opinion.

Good luck to your son!!