These kids are not going to sue OU as if they did, they would have to walk into a courtroom and explain how they have the First Amendment right to say that they want to hang blacks from trees.
Oh, a good 1A lawyer could run rings around OU if that was their only move. Failing to apply the same standards to every student organization on campus could be very damaging in a case against OU. And you know that written publications from other campus orgs, plus statements made in student government meetings, plus statements by Leftist professors in Polysci class, undoubtedly contain way worse and more genuinely threatening comments about white folks, and go unrebuked by the administration.
Some of those parents have deep pockets. If they're smart, they'll sue, and make their pockets even deeper.
What needs fighting here is not the merits of a silly song on a private coach. It's the politically driven limits on speech at a state-run entity.
Racist speech is protected by the First Amendment and they are not violating it unless they threaten a specific individual with bodily harm. Rap lyrics call for killing whitey all the time.