By marginal, he did not mean marginalised. He meant operating at the margins - a reflection of the 'boundary-spanning' role with one foot in and one foot outside the organisation described by James Grunig.
But mavericks? The popular image of PR practitioners is as smooth company men or women with finely honed networking skills. Students will find the concept that PR people can be mavericks hard to recognise.
Jon White described how the PR practitoner often operates alone, giving advice to senior executives that is often contrary to other professional advice they receive. Let's say your company is being prosecuted for polluting the environment. The PR advice may well be to plead guilty, accept one day's bad headlines and work hard to improve environmental protection. But a lawyer's advice would probably be to contest the charge in the courts because a 'win is a win'. (Any PR student should be able to see that you can win in court but lose in the court of public opinion.)
In this context, the advice from PR is out of the ordinary, and it takes a maverick to stick out their neck and defend this position.
(I wear the badge with pride. My first consultancy boss Mike Copland described me as a 'maverick' almost twenty years ago. It wasn't meant as a compliment, but I still take it as one.)