--as I haven't seen any well-designed studies, even correlational ones, addressing it, my sense over the years from many conversations, e-mails, support group meetings, conventions, etc., is that exercise to tolerance tends to improve people who have neuropathy that consists of only or primarily sensory symptoms. These people often have primarily small-fiber syndromes (the small, unmyelinated fibers have only sensory or in some cases autonomic functions) and often ischemic factors, or circulatory factors, are part of the syndrome (as it often is, for example, with diabetics); anything that improves circulation, as exercise certainly does, tends to help move nutrients/oxygen into the nerves and waste products out, and may help symptoms and even healing. I suspect massage and physical therapy may help many such people for similar reasons.

People with motor predominant symptoms, though, tend to to show much less response to exercise--for one thing, when motor potentials are affected, it's much harder to DO voluntary exercise--one may not have the proper pathways to command voluntary muscular action to the complete extent that "normal" people do--and the increased demand on the nerves and muscles is often very fatiguing. For these people, exercise may set up abnormal signalling that results in cramps, spasms, etc.

I understand that many in the MS community report a similar thing--exercise seems to be more symptom relieving/stilling when one has merely sensory symptoms.

This is not to say that exercise might not be having other systemic benefits in even those with compromised motor pathways, but it seems much harder to tolerate exercise in that situation.