You can hardly equate what appear to be consensual adult encounters with "the BBC knew all about his ways".
One is legal. The other is not. If we're going to start berating broadcasters because of hedonism on the part of their celebrities, we might as well just close them all now, and replace all TV with a testcard.
There has been no evidence in the press whatsoever so far that suggests the BBC knew that Hall was engaging in illegal activities. "Immoral", maybe, but morality is relative, subjective, and ultimately irrelevant.