As far as personal experience with litter, clumping or otherwise,
clinging when a ferrets' bottom: I haven't seen it happen.  I know that
most ferrets 'wipe' when they eliminate, which means that healthy ferrets
wipe off any clinging material, including natural litter.  Unlike litters
that use silica, Swheat scoop shouldn't cling so tightly as to cause a
problem.  However, I would be inclined to watch an animal that is
suffering from anal gland problems, or any inflammation of the anus or
genitals.
 
I hope that helps.
 
Gale
 
"Don't smile at me like that!  That's not even a real smile; It's just a
bunch of teeth playing with my mind!"  Lt. Templeton Peck
[Posted in FML issue 4523]