That's a tricky one. <PERSON> was fanatical when it came to his hatred of dark wizards, but he does also strike me as someone who would try to make his students aware of the stakes, and make sure that they were prepared.
I don't know about using the curses on students, but I could see him showing them the curses. That seems completely feasible. You have to remember, <PERSON> was supposed to be as convincing as possible, so it seems likely that even if the real <PERSON> wouldn't do that, his reputation and/or his personality made people who knew him believe he was capable of it. In fact, if <PERSON> had thought it would arouse suspicion by using the curses, he would never have used them.
I could also see him comforting <PERSON>, and probably being even more of a mentor to him than the fake was. As an auror and a member of the Order of the Phoenix, <PERSON> would have felt a sense of camaraderie with the <PERSON> family (he even talks about them when showing <PERSON> the picture of the original Order). He might have even felt he owed them to teach <PERSON> to defend himself and that <PERSON> had a right to be able to take revenge. With his background, <PERSON> might have been one of the only people <PERSON> felt he could trust.
He might even have seen <PERSON> as someone who would hate dark wizards as much as <PERSON> himself, if not more, and could want to train him to be a sort of successor.
To be entirely fair, we like to make antagonists completely evil. 773
<PERSON> might have had a little good left in him when he took <PERSON> under his wing. <PERSON> hated death eaters who were never punished, and his father for not protecting him, but he had no real problem with <PERSON>. He might even have felt a little guilty about what he did to the <PERSON>, even if giving <PERSON> that book was intended to give <PERSON> a clue.
His devotion to <PERSON> may have been because of his long imprisonment in Azkaban, then at his father's hands. <PERSON> freed him from prison, but when he was sent to trial, he didn't show any of his later fanatic devotion, even denying that he had anything to do with the Death Eaters. It may simply have been loyalty. As for the <PERSON>, I always got the impression that it was a random senseless act of violence brought on by poor decisions by <PERSON> than a planned move directed by <PERSON>.
<PERSON> praises <PERSON> several times, and he might actually have liked him as a person, as he never personally seemed to hold a grudge. He only wanted to kill <PERSON> out of his devotion to <PERSON>. It might be possible he genuinely enjoyed teaching and actually cared a little for his students, so long as they were not obstacles to his master. 86