Has anyone been able to verify ADS-B works without radar? I know that one of the biggest advantages of ADS-B is "supposed" to be that it will directly communicate between equipped aircraft without ground support. Has anyone actually seen that in action? That is, seeing another aircraft on an ADS-B display where radar coverage is impossible, say, a remote valley surrounded by mountains with no radar station near.

Obviously both aircraft would need to be ADS-B equipped for this to work.
I can confirm that ADS-B works without radar. I have been involved in several ADS-B trials in areas where there was no or only partial radar coverage. It works. No surprise, it has been designed that way.