I was extremely resistant to the idea of setting dirty eggs--my duck eggs are often FILTHY--but I tried it with one hatch and had a better hatch rate than with washed eggs. So now I just wipe off loose dirt and set the eggs, filth and all.
I wouldn't try the oil--I would think it would plug the pores and suffocate the ducklings. Vegetable oil, and even oil made from animals (which would be from body fat), is nothing like the oil that comes out of the duck's oil gland (which rubs off on the eggs during natural incubation, from contact with the feathers which are regularly coated with that oil during normal preening), nor is it anything like the bloom that naturally coats the egg during the laying process. I would think lanolin would be the nearest substitute, which comes from the hair follicles (or sweat glands--not sure which--it's a by-product of wool production, and it naturally covers wool in the same way that a duck's feathers are naturally covered with oil) of sheep, but I would still be extremely hesitant to coat a hatching egg with it.
If you're determined to try it, you could set a test batch--maybe leave half unwashed, a quarter washed and uncoated, and a quarter washed and coated with whatever substance you want to try. Record the hatch rates and see what you think. If you decide to do that, be sure to post your results here! I'm sure many would be very interested.