Fraternity: That's why people pledge... They're probationaries... Not just for the chapter but themselves as well. If they think they're a better fit with Sigma Nu then they very well may be. I could give a crap what happened at the other house. People can learn from mistakes. Our candidate program is VERY different from the others I know on campus.. well at least the ones I know. Let's just say they usually lose 50%+ of their pledge class and leave it at that.
Employer: People get fired for all kinds of stupid reasons. I'd be interested in their qualifications for what they're applying for more than previous work history. If this is a pattern though then that's something different. When you're checking references most employers won't give circumstances of a termination, they can only say if they'd rehire the person (well that's what I've been told anyhow).
Marriage: I'll jump off that bridge when I come to it... Way too many ifs in that scenario