I think BJWOK has posted up about using a small amount of flash set up hidden on stage, to fill the artist face. You might search for it or PM him. It was a surprisingly nice explanation, just can't recall where it is. But I think it was on here, as i don't do much on Blogs. He tours with bands hired by them for weeks on end.
I used to use flash at a monthly Saturday Night concert by regional bands at a local church. We're friends with everyone there and have known the couple that runs this event for nearly a lifetime. I used to set up lights and rely on flash, worked great, even though a distraction. Super sharp images! Most of these bands are excellent musicians, but have nothing more than smartphone pics on their websites. Some bands really wanted the colors though, so I eventually switched to higher ISO, and sold my (2) 40D's for (2) 7D's.
My last shoot had LED lighting, all Red pointed at the female singers body instead of her face. Horrific to work with but surprisingly nice dramatic images in the end. Feel free to look at my Flickr to see what I've done. The first album is of "Signals"; concert held at a local bar.