CS will NOT affect lipomas (fatty tumors) at all - they need to be removed by surgery, preferably before they grow larger, or become necrotic/infected.
As for kidney function, CS will precipitate in the kidney, causing permanent damage, especially to already compromised organs. Follow your veterinarian's reccomendations, use all prescribed medications and diets as directed. Blood chemistry and electrolyte levels need to be checked frequently to monitor organ function.
As for your dog's elevated BUN without other changes, that can be elevated due to increased protein injestion from the diet and treats. Again, the blood chemistries should be rechecked and evaluated to watch for changes.