A lot of the plants on the toxics list are only toxic if they eat them. If that is the only green thing in with them, they will eat it. If they have plenty of other good stuff, there is a good chance they won't eat enough to hurt them.
I had a hen that spent years camped under a hydrangea bush, but she was free range and was just using it for shade. Many years later I read that it was toxic. The main thing is that they have enough else around so they aren't desperate enough to eat the bad plants. Also some are stupider than others...
Can't help with the butterfly bush. I have one or two around but not in my run.
Sorry