If the guy truly did choose to get a brand, fine. I agree with others that posted before me- let the dad be pissed off at his son, but not the fraternity or school. Brands are essentially no different than tattoos and parents don't threaten to sue the GLO or school when their kid gets a tat.
There is a frat where I went to undergrad that a lot of members choose to get branded. Their brands are on their butts, so it's easy to tell when they got branded cause they bring cushions to class to sit on!

It is not forced and not done on campus and as far as I know, the whole frat is not present, so I really don't see how a lawsuit could be brought against them or the school.
As far as an infection setting in, dying in the hospital, blah, blah, blah.... You could step on a rusty nail, get an infection and die. That's just life.
I'm not bashing anyone's opinion- I just think the dad is angry at the wrong people (frat and univ.) and should be taking this issue up with his son.