I am represented by Daniel Lazar of Writers House. He has sold several graphic novels, the most recent probably being Diary of a Wimpy Kid by Jeff Kinney. My agent doesn't really represent to places like Marvel, DC, or Dark Horse, although he said that if that was important to me, he would try.
He sells to graphic novel imprints of Random House like Pantheon and Scholastic's Graphix. They are more "mainstream" I guess you would say.
Yes, Writers House represent Neil Gaiman as well.
I am not known at all in the comics field, but we've already had interest from some houses prior to submission based on my blog.
During my agent search, I was offered representation by two other agencies who have also had success selling graphic novels.
Because a lot of the mainstream imprints are trying to get into graphic novels as well, I think that literary agents contacts will continue to work. I don't think you necessarily have to be a "name" in the industry, but you really have to think about what you are looking for.
If your heart is set on one of the comic companies--then, yeah, agent might not be the best route. But if you want to look at big publishers, then that seems to be a different animal.
I think you are right about a lot of these publishers wanting "literary" and review-driven graphic novels, but for the Young Adult and middle grade crowd I think commercial works just as well. (Bone, etc.)
Just some thoughts. Hope it helps somebody. If you want the names of the other agencies that offered, you can PM me. I also have a list of agents that I know are looking for GNs.