Pigeon fanciers have used tobacco stems as nesting material. Supposedly it reduces external parasites, but I would have to wonder about long term exposure to nicotine. Look what it did to me.
Chicken shouldn't chaw a plug of tobacco unless they have lost all their teeth. Also I couldn't resist. I imagine it could help with paracites. What specifically do you have in mind? As a topical insecticide I can not imagine why not give it a try.