I read it carefully too. I believe the ad clearly implies that the young men are guilty of rape. If that is a false allegation, it is libel per se. It isn't necessary that the accused young men be listed by name. We know who the ad is about.
The ad does have a short disclaimer: "If they are guilty, I want them expelled." But the rest of the letter dismisses that disclaimer like the insubstantial fig leaf that it is.
It's debatable whether the young men were public figures according to the legal definition of the term when the libel was published. The first amendment protections accorded to speech directed at public figures might not be there in this case.
That doesn't mean a lawsuit would be easy to prosecute and win. And even if the young men were to win, collection on a judgment might be nearly impossible.
I read it carefully too. I believe the ad clearly implies that the young men are guilty of rape.
Don’t forget that some of their professors gave the accused young men bad grades influenced by the ‘perception’ of guilt and other adverse actions. That would certainly be actionable.