Never, ever, at any point in his career or after has anybody come forward with any proof that Marciano benefitted from that sort of activity. I don't think it was ever alleged, other than on internet forums.
That said, every fighter has fights that he is going to win. That's part of being 'brought along' and it has nothing to do with shady connections. That's just how boxing works. Not every fighter is in there to win, even if he is not 'trying' to lose.