What is the ruling on dealing with a mosque imam who insults Sunni scholars, belongs to Sufism, monitors worshippers who disagree with him, and describes them as heretics?

Insulting a Muslim is an act of deviancy (fusuq), and the sin is greater if the insulted person is among the scholars of the Sunnah. This reprehensible act must be changed, either by hand, by tongue, or by heart. If you are unable to change it, then seek another job opportunity, because it is reprehensible to follow a deviant (fasiq) imam, and it has been said that prayer behind him is invalid. If another opportunity is not available to you, then there is no objection to remaining with him while disapproving in your heart.