how has greek life helped you in finance?

A few ways:

• If you go to a target, by joining a Greek org you are self selecting for people who 1) have money 2) like to socialize. As a result, a lot of social rich kids end up in banking, so you have alumni that you can reach out to from past classes or even classes above you that can help you out. As a weird example, I once got on a call as a banking analyst and the PE associate was a guy that was a junior when I was a freshmen in my fraternity. The world can be pretty small especially when you consider that certain schools might target certain geographical regions and similar jobs based on the prestige/ rigor of the school and certain firms considering specific schools as feeders.
• Most banking analysts have no life and many are sharp elbowed and weird. That said, even as an analyst there is a level of social tact required to succeed. Even from the interview stage, a significant number of people are eliminated because they don’t pick up on social cues or behave inappropriately. Honestly, I would say about 40% of people I interviewed that didn’t move on, this was the reason—they were just weird socially. Being in a fraternity can help you learn social cues and how to be less of a weirdo because you interact with others and learn what others find weird or acceptable. Also, with the above point, many Greek individuals end up successful in business because they naturally are just more social people. Social people generally are better at interviewing because they appear friendly and not irritating or odd.
• Greek Orgs can introduce you to a variety of people, which can help you find commonality with others down the line and help you know how to act around certain personalities. I always found people attacking Greek life as lacking diversity to be somewhat ignorant. There certainly can be racial skews and more wealthy individuals in Greek orgs, but how many spots on any college campus has people with different majors, cities, backgrounds, ambitions, all in one place? I found all the other orgs I was in in college to be equally as undiverse and even more so because many times it was all people who liked 1 thing: Basketball for example. Greek orgs you can get artists, jocks, nerds, stoners, etc. 
• Greek orgs can give you social confidence, a hugely important skill for interviewing
• Greek orgs can give you mentors/materials/ study buddies for interviews or classes ensuring you get good grades and understand how to succeed in the classroom and in interviewing
• Greek Orgs teach you how to drink. This actually can be important so you don’t go to a happy hour and make a fool of yourself.
• Greek Orgs teach you how to get hazed and deal with hierarchy. Many kids go to college (especially men) and think they run the world and the world revolves around them. Newsflash, it doesn’t! Nothing quite makes this as apparent as being forced to do an older fraternity brothers laundry or cleaning the floor after a party. Not only is this ego check important for many, but investment banking is just one big haze fest almost wherever you go with a brutally rigid hierarchy. My fraternity sent several people to the hospital during my time there—so did my investment bank. Both sleep deprived me, both had good people and sociopaths in the orgs. The difference is one was supposed to be fun and the other was something I needed to do to pay my rent. A laugh my ass off when I see anti Greek sentiment in the world today because IB is so much worse than nearly any fraternity at this point minus ones at brick institutions with brick leadership (which are the only places where people don’t care about abolishing Greek life).