Yes.. along with so many other things already growing in my backyard.
They really don't care to eat them. As long as they aren't locked into a run with the day lilies with nothing else to eat they will be fine.
My neighbor's poisonous Naked Ladies are spreading like wildfire over here.. along with Bracken Fern, Cala lilies, tansy ragwort, wild iris, butterfly bush, buttercups and so many more!
One flower that is NOT considered toxic or poisonous to chickens is Marigold... eating the petals even gives them darker looking yolk. Sunflowers are also safe and delicious... though maybe fatty.
Please note that "poisonous" or "toxic" are often misunderstood terms... and something that causes mild upset stomach or headache could be considered as such..
My birds actually love hanging out under the butterfly bushes... and the don't enjoy eating them at all... therefore they are left intact instead of picked down to nothing. They quite simply do not consume any of the "toxic" things in high enough quantities to cause issue... when provided with plenty of other forage opportunity.
Now to be clear... I probably would NOT knowingly plant something on purpose that MIGHT be harmful.. and definitely not anything known to actually be deadly... like Oleander or Deadly Nightshade... But please note being in the nightshade family like potato and tomato is NOT the same thing as being deadly nightshade... My birds have munched down tomato leaves to the dirt every season without cause for concern. Not sure if potato leaves may be *more* toxic or not.. just use your best judgement... but try not to let fear mongers make things into what they are not... we can still enjoy many aspects of life.
Day lilies are beautiful! Although I love flowers... I focus all of my planting on edibles if possible.. and try to get things that flower at different times in order to prolong the season of both beauty and harvest... apple trees, blueberry bushes, strawberry plants, blackberry vines, etc... the edible things always require protection until established.
Adding your general location to your profile can help folks make their best suggestion possible at a glance.
When in doubt but still desiring.. I plant out front.
Hope this helps some..