Is Mr. Hale a friend or foe to the Proctors?

Pohnpei's response is correct: Hale certainly thinks of himself as a friend to the Proctors by the end of the play... but it's complicated.  When Hale goes to Elizabeth and begs her to convince John to confess to witchcraft -- fully acknowledging that it would be a false confession -- he argues that the lie is a small sin compared to the greater sin of giving up the gift of life.  Elizabeth, who is virtually a saint in this play, and therefore must be heeded, responds that that sounds like "the devil's argument" to her.

So, yes, Hale is a friend to the Proctor's, but what he's asking Proctor to do is still misguided (Hale has been misguided from the beginning, in one way or another).  He would save John's life, but as we see in the end, 1. damn John's soul (for whatever that's worth), 2. damn John's good reputation, 3. damn the town since if John confesses to witchcraft, it will legitimize the whole idea of witchcraft and the trials will continue.  This last one is probably the most important.