When I was a recruitment advisor, I wore business casual in a color scheme coordinated to the chapter's outfits. I was usually the only alumna on the floor, but the campus where I advised held recruitment in the student center, so we often had alumnae and active volunteers running membership selection materials to and from the house. We asked those volunteers to dress neatly in lettered shirts and jeans, rather than sweats or the usual lounging apparel in the tabulations room.
Now that I'm a recruitment international officer, I wear business casual and my professional ADPi nametag when visiting chapters during recruitment. I also look pretty young and prefer not being mistaken for a collegian.