I'll believe it when I see it. As far as I know, South Korea has not fired arms in protest since the end of the Korean War, and they cowardly rely on US troops to man the front lines.
The US Army has only a single combat division of less then 20,000 men station in Korea. South Korea, by contrast, has a standing army of more than 500,000, with reserves of more then three-million men, split into 52 divisions. And the South Korean military is fairly modern at that. So no, South Korean soldiers are what defend the bulk of the DMZ, with American troops pretty-much an afterthought in actual, immediate military terms. The main purpose of our troops being stationed there is to serve as a guarantee to South Korea that in the event of an invasion, the US will be at their side and not abandon them due to political expediency, as the US has a history of doing to our allies.