What leverage do universities have over sexual violence in fraternities?
As it turns out, membership in fraternities is not, in general, strongly correlated with rape.  Rather, it appears that a large percentage of sexual assault is committed by a very small fraction of men who are deliberate predators, who tend to seek out environments where their behavior is enabled by people either turn a blind eye to their behavior or who are not willing to intervene in a problematic situation.  Some fraternities provide such environments, but many non-fraternity social environments do so as well.

Rape is committed mostly against women who know their attacker and who may even be intimate with them willingly under other circumstances (men are raped as well, but at much lower percentages than women).  One of the major recommended interventions for a college is thus to educate students, especially other men, on how to intervene in situations that are likely to be a prelude to rape.  This is one example of a broad spectrum of recommended prevention and mitigation policies, which appear to be both effective in reducing the incidence of rape and reducing the damage that compounds to rape victims in an unsupportive campus culture.

None of these interventions are particularly difficult or expensive.  The main challenges in implementing them are resistance from people who have some stake in keeping aspects of their campus culture from changing, or who are worried about potential image problems.