Thanks, for the info, everyone, especially the long write-up from Ela.
Looks like except for certain individuals (human) Stevia is quite safe,
but anyone who has low glucose problems or borderline glucose problems in
the direction of insulinoma might find it dangerous -- a consideration for
ferrets.  Risk levels look quite similar to many preservatives from what
has been said, i.e. very safe despite some popular public perceptions.
Given the prevalence of insulinoma with it's increases in insulin
production in ferrets, I'd think that being a bit extra careful for them
might be in order till more is known given Ela's notations that:
 
>A study conducted at the Department of Endocrinology and Metabolism,
>Aarhus University Hospital, Denmark, found that stevioside enhances
>insulin secretion from mouse pancreatic islets stimulates insulin
>secretion via a direct action on pancreatic beta cells.  The results
>indicate that the compounds may have a potential role as an
>anti-hyperglycemic agent in the treatment of type 2 diabetes mellitus."
[Posted in FML issue 3146]