I say no on oil or grease because they don't provide a threadlocking function. Wheels go out of true when the nipples rattle loose at the bottom rotation. SpokePrep or blue Loctite provides a lube function as well as a threadlocking function so that the nipples don't spin and cause your wheel to go out of true. Yet, they provide lube and anti-corrosion function to keep the nipple adjustable at a later time.