Oatmeal is great to use after harvesting in your vegetable gardens. We will till in falls harvest, and plant oatmeal to grow over winter. Come spring, we till the oats into the plot with some rich, composted chicken manure. This system has produced years of great vegetable crops for us.
The oats have a deep root system, so it loads the soil with organic matter, and the nitrogen from the oats/chicken manure get springs crops off to a good start.
I would imagine that steel cut oats/rolled oats would work as an amendment to your organic soil mix, but there are better choices for less money. Alfalfa meal, cottonseed meal, corn gluten meal, soy meal, flax/linseed meal are all good organic fertilizers.
In short, I suppose you could use it, I wouldn't know the N-P-K ratio, maybe you could Google it.