When I built my first UDS, I never seasoned the inside before cooking in it. For the first few cooks I noticed that I would get spots where sooty condensate had dripped from the lid onto the food. This went away as the inside became seasoned from use.
I think that when you have a high moisture environment inside a cooker that some condensate is going to drip on the meat no matter what. A cured seasoned surface will prefent that dripping water from taking anything with it when it drops.