There are those who believe that this is the case, at least according to Wikipedia.
There is a difference between what people do in their own time and what they do on behalf of their employer.
I am sure there are people who do think that. Not sure why that makes it relevant.
Agree that there are differences between what is done in employ and outside, though given that it's not clear thar Bell is even referencing The Merchant of Venice, the action of someone acting in in it would surely be definitely anti semitic to the Guardian, and therefore problematic to them to employ.
Also to switch it, would it be anti semitic for an editor to send a columnist to review a production, and/or for columnist to do so, or would a bad review saying 'Don't go and see this anti semitic garbage' be ok as opposed to a positive review?