Speaking as a physiologist... I do wonder if pain in another location may actually be beneficial in stopping you from feeling the chronic pain. Acute pain usually takes precedence over chronic in your perceptual map of your body so whipping on another area will a) feel nice if you are into pain (not everyone is) and b) take away the thunder of the real pain....

From my experience of BDSM I have learnt that intent and expectation are everything. BDSM play is as much in the mind as the body. There is a marked difference between pain inflicted by a loving Dominant as part of a highly charged sexually heightened scene and any other form of pain. It is not the pain itself that is important but the way it is delivered. I'd enjoy a nipple clamp put on me by a Mistress and hate a random person in the street pinching my nipples.

Also, depending on the cause of the pain, devices like TENs machines (often used in BDSM but actually developed for back pain) can be beneficial if used right.