I don't have any first hand experience with it, but a family member's fraternity blackballed a pledge once. The guy went on and pledged another fraternity...then went on and became very famous in the music industry. The aftermath for them is that they sure wish they had his alum support now.
My husband was president of his fraternity and once had an issue come up where many brothers wanted to blackball a pledge. My husband agreed the guy was far from measuring up and was a major problem, but really dreaded the process of sending him packing... he knew it would bring down a firestorm of trouble because of the guy's family and other connections. As it turned out, the pledge didn't make grades for the second time -- they had held him over -- so they had a clear cut reason for letting him go and nobody could argue about it.