Firstly, i'd like to begin with saying that Van Pelt is not Red John

Now that's out of the way, we can get to business. Van Pelt is the most interesting character on the show IMO. I find it strange that we're into the 6th season now, yet we still know very little, if anything, about Grace's past, whereas every other team member has been given their own backstory-centric episode. We learnt about Lisbon's alcoholic dad, and the fact she acted as a surrogate mother to her brothers, we learnt about Cho's gang and military background, we learnt about Rigsby's troubled past, and we've learnt a lot about Patrick. But nothing really about Grace. All we know is:

- She's from a small town
- Her father is a football coach
- Her cousin is a psychic
- She's emotionally shut down
- She has a bad memory that she's not willing to share, even with Rigsby
- She's fascinated with Visualize and the occult
- She's very capable with technology

That last 2 points for me are important, given RJ's Visualize links, and proven technical nous. We learn the vast majority of those points during the show, in the present, no flashbacks or backstory episodes, again, different from the other characters. We learnt through backstory that Cho is tough, unflappable and very reliable. We learn that Rigsby has a mean streak inherited from his father etc.

Something that dawned on me, from rewatching season 5, she has a lot in common with Lorelei Martins. Both are beautiful women with troubled pasts, both are tough and physically capable, both are easy to manipulate, both would be an ideal target for a serial killer with a cult-ish following. My guess is that RJ recruited Van Pelt much the same he did with Lorelei, harming someone she loved without telling her, and rocking up and playing the hero/shoulder to cry on. 

So my theory is that GVP is RJ's CBI insider (Ron being a red-herring), and RJ's technical expert. Note that RJ only seems to contact the CBI via Grace (like the Dr. Joe N.H part). 

I have no idea who RJ is though.