I don't think it works like that. I know Backstage Pass includes a few street idols like Minami Momochi, but as for the small-but-established groups like Afilia Saga East, I don't think they're part of this.
As far as I can tell, the featured singers are the ones who have earned the most points at the café and therefore are the most popular with customers.
http://p.backst.jp/cast_list.php