I don't think Kirkland is Red John for 2 reasons. However, I'm pretty sure he works for RJ.
When Jason woke up, he asked if he could recognise him. The answer that came from Jason was a negative one, indicating that Kirkland is a friend of Red John and so was Lennon. Come on people,let's be serious. If Lennon knew who RJ is, how come he didn't regonize the man in front of him(if you say that Kirkland is RJ)? I think that RK works for Red john and maybe once he had to do a mission that involved Jason or maybe they met each other at one of the "red john meetings" or somewhere where all the RJ marionettes meet.
And my second reason is the phrase Kirkland said just before killing Lennon "if I ever get in your shoes, I hope a friend will do this for me." Meaning that, if he ever fails on doing something for RJ and nearly gets caught, someone will kill him painlessly before RJ does in his not very gentle way. Because we all know that if Jane was there instead for Kirkland, he would have gotten the answer from Lennon. I know he said something about prison, but I, personally think it was just an excuse or something to say, so he doens't reveal too much.
So, Kirkland is NOT RED JOHN. But I bet all my life belongigs that he works for him.
