I can't really say any artists have made their way to my iPod directly because of the RBN, but at least one has been helped by their presence in the RBN. Eventually it will be at least two.
I first got into the Apples in Stereo after a blurb on allmusic.com talked about the video for "Dance Floor" featuring Elijah Wood. Being a Beatles and ELO fan, it only took one listen to hook me. It was around that time that AiS also began appearing in the RBN. I snatched up what I could there and then got a couple of their CDs as birthday gifts. To any authors listening, I would love to see RB3 versions of the Apples' tunes.
Jonathan Coulton of course was making himself known before the RBN was launched, but I hadn't heard much beyond "Code Monkey" and "Still Alive" before his appearance in Rock Band. I liked those then and I've come to like even more tracks of his now, including "Creepy Doll" and "Chiron Beta Prime." I'm going to get some of his stuff on my iPod Real Soon Now.
PS: I also like Van Canto, especially their covers of "Fear of the Dark" and "Battery."