The SCC is a registered charity run and maintained by the Marine Society and Sea Cadets, unlike the ACF and ATC it is not run by its parent arm. They have a Memorandum of Understanding with the RN which covers things like uniforms, stores, training, organisation and such like. The upshot is the Sea Cadets gets uniforms, stores, some boats, training packages provided at such places like Raliegh, Excellent etc. The RN alos provides us with Senior Staff such as the Captain of the Sea Cadets who is a serving captin in the RN. Each Area also has an Area Officer who is a serving Commander or Lt Col in the RM. They are responsible for orgnaising and monitoring activities and training in their own area. The Navy gets a PR tool. For instance the Battle of Trafalgar parade every year in Traf Square is put on by the SCC and is one of the high profile events of the year, currently the RN could not put on that sort of parade due to manpower commitments.
One of the prvious Sea Lords said that the SCC was one of the RN's most powerful PR tools.
Not sure what the percentage figures (Ninja any Idea?) but there is a fair percentage of recruits into the mob who are ex sea cadets, myself included.
Hope that helps, there is a lot more to the relationship, but that is it in a nutshell, well my defined nutshell. I stand by to be corrected.