If you don't use the oil, the technique is sound. Water should be used rather than the oil In the case of salmon in particular, the fish creates its own oil when it is pressure cooked and doesn't need anything added to it.
THIS IS NOT A SAFE RECIPE!! YOU CANNOT SAFELY OIL-CAN ANYTHING AT HOME, EVEN IN A PRESSURE CANNER. If you use this technique you must store in the refrigerator and eat within a week. This is a biohazard waiting to happen!! The oil is too dense for the heat to effectively penetrate to destroy any food poisoning agents. Please be very careful with this recipe. It is not shelf stable.