We've been giving it to them and it isn't even winter yet.
I make steel cut oatmeal in the crock pot almost every night, and there is always some left in the bowl, which goes to the girls. We had one really frosty morning, and I was low on kitchen scraps, so I did make them their own bowl of normal oatmeal that day.... spoiled chickens.
I think as long as it is real oatmeal and not candy oatmeal you are good to go.