Please correct me if I am wrong but I believe the answer is yes. However there are campaigns out there in which the managers only look at the number of posts in the profiles, so it is clear that they are not bothering to read any of the posts. Should those campaigns be allowed? Does anyone know any of those campaigns?
They must, yes, and, besides, it should be far more easy to mod the campaign managers than the posters, for obvious reasons.
But, sadly, this is not happening in every campaign, at least for the moment. Anyway, most of the shitposters are related to bounties instead of signatures, but, still, there are shitposters related to signatures due to the number of posts you have to write weekly.
Notice that not all the people wearing a signature is a shitposter, as well as not all the people without any signature is a good poster.
Nevertheless, I agree with you. Campaign managers should be dedicated to mod the posts of their people in order to help to clean-up the forum. But, for the moment, there's not such a requirement, I'm afraid.