If you look at the openings in your intake plenums, you'll notice that the holes are not above #1 and #2. As a matter of fact, they are probably the furthest from the intake.
Air, or in your description, oil, would enter through the intake valve so it wouldn't hurt the injector. You could fill the cylinder with oil while running and it wouldn't hurt the injector. You'd probably end up with bent/broken rods and a hole in the side of the block, but the injector should be ok.
Give us more information on your truck. How many miles? Original injectors? Any mods? How does it run? Is it burning any oil? Did fuel mileage go South? How long have you had the truck?