Well, coming from another guy in the seminary, I would say that its an issue that is kind of relative the the situation. Its impossible to say it is wrong/right without looking at the given situation.
If its a guy who has some of the same problems that any other guy goes through, I personally wouldn’t say anything. That can be left up to bishops,vocations directors, the seminary administration…etc.
If he isn’t called to the priesthood, it’ll probably show up eventually during seminary. Keep in mind, folks, that while in seminary, every single little detail about a person is scrutinized and examined, so all the bad stuff USUALLY comes to the surface.
BUT, if there happened to be an issue that you knew this guy is hiding from the Church in order to get into seminary, then of course I would say something to him. One on one, and in privacy of course. And it would have to be a pretty serious issue. Like murder. maybe not murder, but you get the point. Otherwise, I would just chill and let God work it all out.
And keep in mind, that if its just something from the guy’s past, he could very well be over it by now. But again, it all depends on what it is that you happen to think should keep him out of seminary.