Our chickies loved the dry oatmeal, too. They'd eat it before they'd eat the chick starter. I also read somewhere it was good to give them the dry oatmeal if they had pasty butt, that it helped make their poo less messy, and it sure seemed to work with ours. No more pasty butts, just lots of very happy chicks!
You needn't worry if you make oatmeal with milk, milk is apparently quite good for the chickens and I believe it's in most of the chicken feed I've seen, though I'd have to double check the bags to be sure. Most of the "homemade" chicken feed recipes online put powdered milk in the feed for them. Gives them calcium, protein, and other nutrients they need.
On cold days, I've given our flock warm plain oatmeal, sometimes with some cornmeal mixed in, or even leftover cornbread chunks and leftover beans from dinner. They absolutely love it! You get to hear all those happy little chirps and purrs and stuff when you feed them yummies. I love chickens and chickies!
Enjoy your babies. Toss in a few clover leafs (individual leaves, not the whole clover) and watch them go crazy! Chickie rugby!