Well the club can allow anyone they like to broadcast matches, and Linnell does the post match meet & greets in the corporate section - Guess who pays for that?
Quite frankly he is so biased he may well be in breach of the BBC's code of conduct. Certainly he seems to be gaining a lot of resentment amongst fans over his disgraceful stance.
It's only 'disgraceful' because you disagree with it. No doubt if he was rabidly anit-SISU you wouldn't be complaining about him being in breach of the BBC code of conduct, you'd probably declare him to be fair and balanced.
Some people just can't stand the thought that there are people out there who disagree with them. That's life, get over it and stop crying.