No, you should not cook oatmeal in your pressure cooker. Oatmeal is one of the foods that foams and sputters excessively during cooking. This foam can clog the steam vent, which is the pressure release device.
A clogged vent is a serious safety risk, as it prevents proper pressure regulation and can lead to dangerous excess pressure buildup. For safety, you must avoid cooking any foods known to foam, like oatmeal or applesauce, in a pressure cooker.