I don't know what sort of emissions testing (if any) they have in PA. If it's just a sniffer test, it may well be possible for a properly-running engine to pass the test without cats in the first place, and he's getting by. However, if they do any visual inspection, he'd be up a creek.

The secondary/lower cats have nothing to do with passing any sort of emissions. Nissan now builds all their vehicles to the California emissions specs.
I don't know if he kept them in place on his truck or not, but it's a 2001 or newer and would have had all 4 cats before the headers were installed.

SLR changed the supplier/builder of the headers after the one that the member here (perna as I recall) bought and found to be defective.