Hi Lance,
I've never used it, or seen it for that matter. But I did find this:
"SODIUM CASEINATE - used as a binder in products such as frankfurters and stews."
From a
USDA site about addatives in meat and poultry products.
If it's listed soley for franks, I would skip it unless you're making emulsified sausages and are having trouble with texture or fat/meat separation.