Is it permissible to pray behind an imam who writes amulets that some people believe save them from sorcery and the evil eye? And what should one do if it is not permissible, given that there is no other mosque in the village?

It is absolutely impermissible to wear amulets, even if they contain Quranic verses, due to the generality of the proofs for their prohibition, as a means of blocking pretexts (sadd al-dhari'ah), and due to the potential for them to be exposed to disrespect. If these amulets contain polytheistic elements (shirk), then it is not permissible to pray behind the one who writes them. If they are free from shirk, then the validity of praying behind him is a matter of dispute, and the more cautious approach is to prohibit it. As for an Imam who claims knowledge of the unseen, practices magic, or supplicates to other than Allah, it is not permissible to pray behind him.