Artificial sweeteners and butter aren't very good for diabetics, though oatmeal itself is. The presence of insoluble fiber from steel cut oats and the like is great for the digestive system and insulin regulation. Oatmeal is also pretty low of the GI index, meaning it takes longer to digest. It's sustained release energy.
If you want to sweeten it, use cinnamon instead of artificial sweeteners which can actually spike your blood glucose levels. Cinnamon is much healthier and also controls blood sugars. As Morning Glory mentioned, almond milk is a better alternative than butter. Better yet, use almond butter! Low GI, super healthy, and the protein content gives it staying power.