I'm not really following your argument here. You seem to be over-complicating the Haslam gossip by getting bogged down in whether or not it would be libel.
The point that's being made is that if Haslam and Marr had actual evidence of Morrissey having done something illegal, yet had just sat on that evidence and done nothing, then whilst not being complicit in Morrissey's hypothetical crime, they would surely be complicit in withholding evidence of/knowledge of a crime. Isn't that a crime in itself.
And if they have no such evidence ( as seems more likely to be the case) then Haslam is, of course, talking out of his arse, and obviously isn't going to elaborate on his hints, because he'd have no evidence to back up his claims - which would, of course, be libel.
So I don't really see anything complex about this.