Hi Geoff,
Yes having a blaze indicates the presence of the Waardenburg gene, which
leads to a known "syndrome" in many animals including ferrets.  The
expression of this gene varies.  It can be in markings such as the blaze,
plus a host of other white markings.  The presence of this gene does
predispose the ferret to congenital deafness.  Not all blazes are deaf.
But many are.  I have a web site that describes all about the WS markings,
and also all about deafness.  There is a page with photos of markings, a
training site, and also a testing site.  There is host of information on
their.  I think many of your questions will be answered there. :)
 
Wolfy
Please visit:
http://www.geocities.com/wolfysluv/
for information on ferret deafness:
http://www.geocities.com/wolfysluv
[Posted in FML issue 3357]