is it possible for english teacher to use english without mother tongue everytime he/ she teach?

In my opinion no, because what? In each class consists of many disciples, and not all students understand what is conveyed by the teacher if the teacher to use English entirely. And teaching and learning activities were less effective. It is also possible to use English teachers alone entirely, but it pertained to the class of superior class, which most likely explanation of all the students familiar with teachers who use English entirely. For instance my class, if teachers use English entirely, not all students understand, and sometimes even to certain things lecturer delivery using the Indonesian language. for what is described is understood by students

which one is better english is taught by native speaker or english teacher?

I think better to learn english to english teachers a lone , rather than to native speaker. Because , i think are more teachers know his grammar,stucture. Whereas the native speaker in my opinion is only good in speaking , he can speak well but not necessarily correct grammar and structure of this . Talking to native speakers is a great way of improving your spoken english , but native speakers of then don't ralize that things they consider" simple " may be very difficult for english learners.