Chickens are immune to uroshiol, the oil in poison ivy that causes allergic reactions. So they can eat that stuff with no ill effects. They're generally smart and tough enough to avoid getting hurt on thorny plants, so the raspberries are not much of a danger to them.

I'd dig up the raspberries and move them, since they're more far valuable to you than as chicken feed. Brambles transplant very easily, so you can probably expect a good success rate with transplanting them. Find a new location that gets similar sun exposure to where they're at now.

Are the chickens going to stay in this area all the time? The main concern I'd have would be if they are ranging the rest of the property, they'll eat the poison ivy berries and litter the seeds in their droppings all over the place and spread the ivy to new locations. Also, if you're handling the birds, the uroshiol oil can transfer from them to you and give you a rash. You can reduce that by always washing (scrubbing with a washcloth) your hands and arms after handing the chickens to remove the uroshiol before it absorbs into your skin. Over time, the chickens will probably kill out the ivy by eating it all, reducing the need for these precautions in the future.