black walnuts to pigs
According to my three references on toxic plants, black walnut does not seem to cause toxicity in any animal other than horses. Horses are very susceptible to black walnut toxins.
I do not know how well the pigs will digest the nuts in the hull but it should not cause any illness due to the toxins in the plant. Black walnuts have a particularly hard shell compared to other nuts and acorns so they would need to break them open well in order to get at the nut meat. Wet nuts are high in moisture and low in dry matter so they should be fed with other drier feed. Nuts are high energy sources due to the oils.
I don't have an answer for the teeth.