Piedmont does ground handling for the US Airways express ramp in DCA. Mainline US Airways and republic flights are handled by mainline agents above and below the wing. They will both ramp up hiring in the near future because of the new slots they are acquiring from Delta. In fact I think they are hiring for it now.
Career Opportunites - Piedmont Airlines, Inc.
https://usairways.greatjob.net/jobs/...f-721262a4b140

You can try DGS or regional elite but I don't think you get any travel benefits with them.