I had to ask my wife about this one, but she has never seen 教士 before. She tells me it's not a word.
Actually, 教士 is a valid term, although it may be considered to be jargon within the budo world:
The first few sentences from the above article states (my quick, loose translation) that the term 教士 is a title awarded by the Dai Nihon Butokukai with its rank just below that of 範士 (hanshi) and just above 錬士 (renshi).
Hope that helps,