Johan would not be part of the Druidic initiation/oaths, no, at least not specifically. As you said, he's one of many, and really, he's just a buyer. It was the adventuring population that was directly responsible for the deaths of all those animals, not Johan.
Fanatical characters are, however, allowed to believe whatever they wish, of course.
Within the Druidic order, there will be those who will applaud the killing of Johan, while others may see it as pointless to kill out of revenge after the animal that Johan sought was already dead, and still others wouldn't care one way or the other.
The Druidic order, as a whole, neither sanctioned, approved nor condemned the murder of Johan, and it did not have any sort of bounty for doing so.