It depends a bit on how good your valves are and how much oil they need. Some valves work a lot better when evenly coated. Some a drop of oil will work. Oil, on the valves and in the leadpipe will help prevent oxidation. Even Monel, while being highly resistant to oxidation can oxidize. Oil helps retard that.
I actually think pulling the valves up and giving them a good oil is a good thing. It oils the valves very throughly and this is good for lubrication and protection. Does it scratch the valves? I don't think that would be a problem it you handle them carefully. Monel is not only oxidation resistant, it is quite hard.
Being primarily a tenor player (trombone) I have thought about it a bit. The slide is being moved great distances all the time. Trombone players "ram" the slide once a week or more to remove grit and dirt and build up. Then put slide cream or a very thick oil on it. That stuff attracts dirt. Years of moving the slide, talking it off and cleaning it, putting new lube on it, and a slide will STILL more likely oxidize than scratch.
As for red rot, I always recommend Herco's spitballs. Blow them through the horn a couple times a week if you play a lot (or marching season for some). It gets the silva out. I blow one through about 6 times, then put valve oil on the spitball and blow it through a couple more times to coat the inner slides, tubes, and leadpipe with oil -- helping to resist red rot. I hold down the vales so the spitball goes through every tube.
Jason at Bells Superlube (
www.bellssuperlube.com ) made his oil come in a spray bottle -- no precision application for Superlube! Why? Because after being a trumpet tech for years, he determined that even the best valves need to be throughly coated. You have to remove the valves and spray them away from the horn (oil goes everywhere). But boy do the valves get a great coating.
Food for thought.
Jim