Yes, it is permissible for one person to take care of reciting the adhaan and leading the prayer. If the muezzin has more knowledge of Qur’aan than anyone else, then he may lead the people present in prayer as the imam. The same applies if the usual imam is absent and appoints him to act in his stead. It is also permissible for him to be appointed as the regular imam. End quote.
Shaykh ‘Abd-Allaah ibn Jibreen