In the Harry Potter universe, the DADA job is portrayed as cursed and each person can only have the job for one year. However, Lupin seems like a really good teacher and I would have expected him to have taught at Hogwarts before. Did he or any of the other teachers Harry had taught before? It doesn’t have to necessarily be Hogwarts that they taught at before.
EDIT: I understand the question wasn't very clear... I meant had any of the DADA teachers Harry had before ever taught DADA before?