Despite the interesting quote from Mashburn, "I have a lot of friends. Sheriff's Department, mayor's office..." I really don't think he is RJ.

I'll tell you why... Yes, he has a ring on, but it's on his RIGHT hand (ring finger)

Mashburn is NOT afraid of heights, as noted when his car runs off the edge of the cliff in episode 13 season 2.

I know that some people have referenced Dr. Miller's list of patients and the fact that it had someone with the last name Washburn on it, but that's too far a stretch in my opinion. Why would they replace the M with a W it's just a really silly thing that I don't think means anything at all (people are reading too far into it!)