Once, yes, but I wonder if that is true anymore in these days of $60k+/year fees. Do universities make more from undergrads or alumni donations these days? Because if their goal really is successful graduates then they are not setting their students up for success by policing every dispute. It would be completely different obv if YikYak was the "official" app on campus, but the university administration is nothing to do with it, and wouldn't have the power to block it even if they were. What are you expecting them to do exactly?
If a crime has been committed, go to the police, the real police.