George,
It could also be the sural nerve or a whole host of other things. This link shows diagnostics and things to check.
Foot numbness
Diabetes may be a risk factor for bladder cancer (slight increase in risk), but not the other way around that I've found any information on.
http://www.springerlink.com/content/420u2vpw14415ru4/
Surgery itself seems to have an impact while recovering because they always check and give insulin, if needed. I'm not diabetic but I was in during my recovery in the hospital. A few months after, I got tested to be sure and there was not a problem.
My surgeon said it's common to have blood sugar out of whack during post-op surgical recovery.
Mike