Here’s the deal with Fraternities and Sororities:
Each schools local chapter is given a charter by their National fraternity but they basically take care of their own recruitment, pledgeing, finances and house maintenance. Their commitment to the National headquarters and their bond with other chapers more or less consists of wearing the same letters, paying dues and following the same pledge book (basically a book containing the history of the fraternity and other stuff) and dealing with the occasional hard-core National rep super-lifer. Local chapters, in fact, often resent intrusion into their daily lives by the National.
For the most part, chapters generally have a free hand in how they run their house, unless they violate the rules of the National fraternity such as failing to maintain grades or membership levels, commiting some crime, violating national hazing statutes (or in the case of DZ, apparently being fat and/or ugly). Houses can also be kicked off campus by the school for violating campus rules as well.
Chapters of the same fraternity can be very different from school to school. My chapter basically was more or less a bunch of well rounded, not particularly evil preppy J Crew clones who liked to party and were involved in a lot of stuff on campus (fairly typical fraternity profile). Other chapters of the same fraternity were 'roid addicted meatheads who took to branding themselves.
I understand DZ’s desire to improve the strength of their chapter. My schools DZ chapter had the same exact problem and eventually they couldn’t maintain enough members to keep the house open. Evicting 2/3 the house, however, is completely inapropriate and gives a bad name to Greeks everywhere. They should have either pulled their charter and let them go about their business as a local sorority (not affiliated with a National) or work with them to actively improve the house. The whole house turns over in 3-4 years anyway so eventually the problem takes care of itself.
Sororities, in my experience, are very different from fraternities. At my college, fraternity “rush” (the recruitment period) lasts officially 8 weeks but starts unofficially as soon as freshmen start showing up to your parties and meeting your brothers. It is basically 8 weeks of open parties, scheduled social events (paintball, bar-b-qs, whatever) and basically informal hanging out until we figure out if we all like you.
Sorority rush consisted of 2 weeks of a rigid, formal, structured program of playing dress-up and meet N’ greets. The girls get dressed up and meet each sorority for like one night. At the end, each submits their top picks like the NBA draft. If your pick matches the sorority, your in. Problem with this method is that you basically have to instantly figure out if you belong in the stereotypical JAP house (Alpha Phi), WASP house (AXO), hippy house (DG), jockette house (Gamma Phi) guidette house (AGD), cute and preppy house (AOPi), nerdette house (Theta) or ugly house (DZ). At least with fraternity rush, you have weeks to figure out if you like being with the jocks, stoners, rich assholes, etc.