As far as who Red John is, personally I dont think its any of Jane's suspects. However I believe without a doubt that Van Pelt is working for Red John, we are getting far too close to the Red John reveal and the side story continues to be her relationship with Rigsby which honestly makes no sense due to the fact that there they are not moving the story along at all.

We know very little about Grace's past but the little we do know is that she had a bad childhood, as Red John did with Kirkland's brother and so many others he probably helped her and now has her on the inside. The fact that she got married recently has firmly established in my mind that she is the mole inside CBI otherwise the producers wouldnt have written that in, it is all setting up the audience to feel betrayed because they are pushing Van Pelt and Rigsby's  relationship.

She though is not Red John I've heard all the theories about her Red Hair and the fact that the literal meaning of John means GRACE and mercy but I dont buy it shes too weak of a character to be the serial killer