No. It isn't. Troops "counter Chinese influence" by promising to defend against a Chinese attack. If there are no troops. than South Korea bends its policies to make sure that the Chinese never even think of attacking: thus China has "influence." If there are troops, then South Korea has to worry less about keeping China very, very happy.
If there is no danger of and no fear of a Chinese attack, then troops are an extremely ineffective and expensive way of countering "influence."
Whether U.S. troops in countries near China is "hegemonism" kind of depends on who you are. If you are one of China's ruling elite, it certainly is "hegemonism." If you happen to live in a country on China's borders, it looks more like "anti-hegemonism." Every time I talk to a visiting delegation from Vietnam, I keep expecting that one of these years the U.S. fleet will be invited back into Cam Ranh Bay (and I think that the U.S. should decline--that if you want U.S. defense, you need to be a political democracy)...
Brad DeLong