The term Rho Chi was used to signify NPC Recruitment Counselors. The NPC did away with the name Rho Chi recently because another Greek organization had the name Rho Chi. Names for these counselors can vary by campus: Pi Chi, Sigma Rho Gamma, Rho Gamma, etc.

From ariesrising3's Greek Info Pages:

Recruitment Counselor - A member of an NPC sorority who disaffiliates from her sorority for the duration of Formal Recruitment. She will assist the PNMs during the process of Recruitment, answering questions and running a Recruitment Group. They cannot reveal their sorority, so they remain neutral and don't influence their PNMs. They are revealed on Bid Day.

ETA: After a sorority member has been initiated and becomes experienced in recruitment, she is able to apply to be a Rho Gamma. Those on the campus' Panhellenic Council select the women who will serve as Rho Gammas for the next Recruitment.