I don't remember where it was unfortunately but I can tell you my ducks and chickens have been eating ornamental sweet potato vines almost daily for months and they love them.
Amanda, I'd love to see the sites you found to verify. I, too, have been frustrated by the variety of information, and I don't know who to trust. My chickens pretty much left the sweet potato vine alone until one day they seemed to "discover" it, and they ate an awful lot of leaves all in one day. I've kept them away from it all week, and no ill effects I can see. Anyway, did the research you did distinguish between actual sweet potato vines and "ornamental" sweet potato vines? Ours are the ornamental variety. Thanks in advance!