This past fall, two of our new members were RAs in the freshmen girls' dorm, as well as two active sophomores. Additionally, when I was a freshman living in that dorm,
my RA went through fall informal recruitment and was a Pi Phi new member - none of the other RAs were in sororities.
I really looked up to my RA and she had such a good time pledging Pi Phi that, to tell the truth, her experience made me want to be a Pi Phi, too! She was always coming home with gifts from her big sis.
And, needless to say, we had a lot of girls from that dorm become Pi Phis this year because they bonded with their RAs who were Pi Phis - but many chose other houses, too.
At Hillsdale, we don't have a system in place where the RAs must disaffiliate (I believe that's the proper term) for the year or semester. Our RAs are more than welcome to represent their Greek affiliation by attending house events, wearing letters, having paraphenalia in their room, etc. Panhel, however, keeps a close eye on the dorms to make sure nothing shady is going on.
If you have a positive recruitment and new member experience, regardless if you are allowed to inform your dorm-mates of your affiliation, then your experience may lead other girls in the dorm to want to go through recruitment, too. Thus, I could see the whole experience having a positive effect on everyone.
Good luck with recruitment!!