1. They did have to move out of the greek dorm, most of our Pi Chis were older though and did not live on our floor. If they lived in an apartment with other sisters or a mixed group of sorority members they spent a LOT of time in their room and never mingled in public or in sight of others.
2. I don't know that there was ever any sort of intentional shuffling of PNMs because they were close with Pi Chis, but I wasn't a Pi Chi. But for example a younger sister of a Pi Chi was going through recruitment, I'm fairly certain they kept her out of the group.
3. You really want your ass handed to you by a bunch of 18 year olds who are wound up and under extreme pressure? Go for it