Do you want to participate in ROTC to commission as an officer? If so, you must renounce your Korean citizenship, which excludes you from service. I also assume that serving overseas regardless of the relationship between Korea and the States is always a red flag.
Also, if you are going to renounce your Korean citizenship, it's important that you also notify the Military Manpower Administration at the consular office or embassy. They have a liaison officer at each one and it can help you when you visit family or whatever in Korea. One of my cousin's friends was arrested at the airport because he was still marked in a government database as someone who had not fulfilled their service yet, even though they renounced.