Rob Bartlett used to do some comedic commentary when Monday Night RAW first started, and like you said, Pettengill was involved also, so there IS a history of McMahon recruiting radio guys. However, that was back when RAW was done from New York EVERY week, not all over the country like RAW and SD are done now.
Also, both Pettengill and Bartlett were basically just "throw-ins" on the telecast. In the case of Smackdown now, whoever replaces JBL will be the driving force behind putting over the talent and moving the storylines along. I don't see someone who is doing it as a "side-job" getting the gig.
BTW, McMahon also had Opie and Anthony doing some XFL pre-game show live from the now defunct WWE restaurant in Times Square.