Well...certainly, congratulations are in order. Glad he got work in his chosen profession and I wish him luck.
That being said: there's a LOT more to being good on the radio than having spent 6 months as a stunt/sidekick on a (arguably, failed) morning show. One of the hard adjustments to make is the discipline required to, daily, make liners and station positioning sound fresh, particularly when the sum total of your experience has been mostly free-form morning show yacking it up.
Since there's no shortage of people who'd kill for a live on-air gig, whatever "cachet" that's being brought to the table courtesy of the 99X experience had better parlay itself into good, consistent on-air work. Or he'll be replaced, and fast. If he's smart, he'll take direction from his PD and do what he's told. In my experience, this is hard for ex-morning show second and third wheels to do, because most of their "training" came courtesy of the usually insane/anti-management/over the top ego of the main morning person(s) they were working for. Respect for PDs is typically in short supply with those folks.
I'm not saying this is impossible for Fat Kid to do--not at all. Just that it's something he really needs to concentrate on in the short term. Best of luck and I truly hope this works for him.