I'm not surprised that RAs have to disaffiliate. After all, RAs have just as much influence, if not more, over their residents as Rho Chis do over their rush groups. It would be frustrating to have an XYZ RA who's convinced all of her residents that the XYZs are the coolest before rush has even begun.
As we've discussed before, the use of numbers in rush threads is to protect the rushees from getting cut, not just to protect the sororities from having their feelings hurt -- so numbers are the safest thing for rushees to use.
Of course they can use whatever they want, though.