One important distinction to make is whether your "prostatitis" is truly a prostate problem or a form of Urological Chronic Pelvic Pain Syndrome. In my first bout with PVP (8 months after my vas in March 2005), I definitely had something going on with my prostate. I say that because my PSA ran from 4.2 to 4.5.
Since my reversal, I haven't registered a PSA above 0.3, yet I've had two separate relapses of PVP. In 2008-09, my relapse was only in the scrotum and went away after 6-7 months on Celebrex and Gabapentin.
This bout, just about over, has lasted 13+ months and I definitely had some pelvic pain going on. In fact, the worst of the pain was in the perineum, and that took extensive pelvic PT and Elavil to get control over.
I think there's a whole web of inter-connected problems that can and do start after a vasectomy. No one has an incentive to make the connections because it'd kill the golden goose of the vasectomists. A couple guys here like Aschiro and Choohoo know more than I'll ever know.
But, I think one key is to find out if your prostate is truly part of the equation. Prostatitis is a poorly conceived, catch-all name that the Cleveland Clinic has stopped using for non-prostate pelvic pain.