According to the documentation http://docs.moodle.org/en/Hub_administration hub administrators are respondible for hub content. People should be able to contact the hub admin easily to report any problem content.
Currently, a hub admin may be contacted by clicking a little envelope icon next to a course creator's name, then logging in to the site, then selecting hub administrator from the 'Send to' dropdown menu i.e. it's not easy to find!
I suggest that we have a contact us link on the front page of the hub site, perhaps a contact us block.