What is the status of an imam who knowingly performs the Nikah of a Muslim woman to a non-Muslim man?

Answer

The 'imam' who conducts such a kufr ceremony becomes a murtad. Salaat behind the murtad, scoundrel 'imam' is not valid. In aayat 10 of Surah Al-Mumtahinah, Allah Ta'ala states:

"O People of Imaan! When there come to you Mu'minaat who have migrated, then test them (to ascertain if they are indeed Believers). Allah knows best their Imaan. Then, if you know (establish) that they are Mu'minaat, then never return them to the kuffaar. They (Mu'minaat) are not lawful for them (kuffaar men), nor are they (the kuffaar men) lawful for them (for the Mu'minaat)."

Nothing overrides the Qur'aan. The Qur'aan and the Ijma' of the Ummah categorically prohibit marriage of Muslim females with kuffaar males.