Praise be to Allaah.
Undoubtedly this person is a fortune-teller who uses the shayaateen and gets close to them by doing things that they like so that they will tell him some concealed things. He may be offering sacrifices to them, calling them by name, obeying them by disobeying Allaah and eating haraam or impure things, etc. Of course this is kufr and shirk. He must be asked to repent, and if he repents, all well and good – otherwise he must be executed. It is not permissible to pray behind him or to greet him with salaam until and unless he repents. And Allaah knows best.