No, not really. The RCC is insanely crowded and run down (worst in the entire UA system, IMO), and the Sen lounge (which your *G card will allow you to use) is nicer but just as loud and crowded.

If you really want sleep, just walk over to the Sheraton that is inside the airport (across a walkway from check in) and get a day room. But for 6 hours, I doubt that is really worth.