What is the view on the Ibadi sect, and is it true that Ibn Baz (may Allah have mercy on him) declared them disbelievers, and is it permissible for one of them to lead the prayer?

The Ibadiyya are one of the deviant sects due to their rebellion, aggression, and revolt against Uthman and Ali, may Allah be pleased with them both. It is not permissible to pray behind them. It is not permissible to allow the people of bid'ah (innovation) that amounts to kufr (disbelief) to lead the prayer. Whoever finds an imam who is not an innovator should pray behind him, not behind the innovator. Whoever finds only an innovator should advise him, hoping he will abandon his innovation. If he does not accept, and his innovation is shirk (polytheistic), such as one who seeks help from the dead or supplicates to them instead of Allah, then one should not pray behind him, because he is a disbeliever, and his prayer is invalid, and it is not correct for him to be an imam. If his innovation does not amount to kufr, such as uttering the intention aloud, then his prayer and the prayer of those behind him are valid.