While anything is certainly possible, I would tend to doubt it. The path
that the sciatic nerve takes doesn't bring it anywhere near the prostate,
IIRC. Of course, if it is a question of some type of inflammatory process
that is affecting both, then who knows.

The nerves that control the pelvic region eminate from the lower end of the
spine (below the sciatic nerve).  I believe nerve compression in this area
can cause reffered pain to the pelvic region in a mannor similar to sciatic
nerve compression causing pain in the upper leg.  Nevertheless, these are
seperate nerve groups.  It's also not a wide-held theory for causing pevlic
pain.  Look into pelvic floor muscle disfunction
http://www.chronicprostatitis.com/myoneuropathy.html

I'm no doctor, so get a professional opinion.