Yes, so in this case, these white kid's First Amendment rights to free speech were indeed violated.
It depends what the policies were put forth by the university regarding fraternities and racism. Until we know that, its impossible to say.
Similarly, colleges/universities have banned hazing. Perhaps this university has banned the overt expression of racism by fraternities. Again, I do not know the policies of the University of Oklahoma.
For example, plagiarism is against the policies of all higher institutions. If youre caught plagiarizing, you will most likely be dismissed from school. This is stated in all the handbooks of higher institutions. If the same thing is listed for fraternities regarding racism, then they will be dismissed. Plain and simple. If not, then I am assuming they can sue.
If you're this concerned, find the policies and procedures handbook put out by the University of Oklahoma and see what they see about policies regarding fraternities.