Don't fool yourself, chickens will eat most anything and I wouldn't give the grounds to them, there is absolutely no food value in it for them. Why would you think of something like this? Humans give their bodies all kinds of things they shouldn't but why make animals do so? (I'm a heavy coffee/chocoholic but I sure wouldn't advocate it to anyone else, human or creature!)
I doubt they will eat them and if they do...doubt it will hurt them. If you are composting them, I would not let the girls in the compost pile either if you are using food scraps in the compost. There is a chance of botulism.
Have you ever seen the things chickens and other animal will eat? Even those animals that are fed very very well that still eat the nastiest stuff you can imagine? I think we are over protective. There are sustainable living farms that never feed chickens the way we think they should beed them. They have to scavange from compost and other sources of free range food. They tend to have some very healthy birds in their flock. Botulism is one of the last things I worry over when it comes to chickens and their need to tear apart a compost pile. Is it possible they can pick up botulism poisoning, yes. Is it likely, not as frequent as we think.
I would not give them the coffee grounds. I save those for my garden and big flower pots of acid love plants.
I also use them in my homemade soap for foot scrub bars.