Before he appeared in Salem, had Hale ever found a witch?

No, he'd believed himself to have found evidence of a witch, but was then proven wrong.

"Like almost all men of learning, he spent a good deal of his time pondering the invisible world, especially since he had himself encountered a witch in his parish not long before. That woman, however, turned into a mere pest under his searching scrutiny, and the child she had allegedly been afflicting recovered her normal behavior after Hale had given her his kindness and a few days of rest in his own house. However, that experience never raised a doubt in his mind as to the reality of the under-world or the existence of Lucifer’s many-faced lieutenants."