Yes, chickens are not horses. The walnut leaves or hulls won't hurt your chickens.
I've read different things on the Juglone: which parts of the tree have it, how long it takes to break down, and whether any is left after composting. I personally do not use leaves, hulls, bark, or any part of a walnut tree in my compost or garden.
Your chickens will not be able to open the nuts to get to the meat inside. They are too hard to peck open and too big to swallow and get into the gizzard. Black walnuts are probably too big to be ground up by the gizzard anyway.
Physically, they won't hurt your chickens, but I would not put walnuts in the run anyway. I'm mainly talking about the husks. When they are green or even after they dry up but them get wet again, they stain real bad. If you put the husks in the run and it gets wet, I'd expect your chickens to have stained feathers and feet. They probably would not track that into the nest and stain the eggs, but many people would not like stained chickens. And if you handle that stuff in the run when it is wet, you could stain your hands or your clothing.