I have also had a ferret with no external genitalia.  She never had any
issues with this, and lived to be 7 plus before we lost her to lympho.  I
never thought much of it, and figured if it's not broke, don't fix it.  I
figured it was just one of those flukes of nature like being born with
webbed toes or not having cartilage behind the ears.
 
Had she had problems with infections, I of course would have looked further
at various tests.  Also, I use pelletized recycled newspaper litter, so
didn't have a problem with clay stuff getting up inside of her.
 
-Anne
[Posted in FML issue 2483]