Can a Korean-American be stationed in S.Korea?

Yes they can be posted there, and translation skills would be sought after.

If you can Han Guk Mal hamnida chadisaiyo, you are almost guaranteed to go there if you ask for it or even if you don't. Make sure you have an MOS that is used there. Since it is a short tour for many soldiers, the attitudes are often lousy and morale suffers. The rules are often set for the lowest common denominator (others ruined a good deal decades ago). If you score high enough on the language test, you'll get extra pay. They will use you often, more than you might want. I have many Korean-Americans friends who missed out on seeing many other foreign countries since they were always needed as translators in Korea first. Kham sah hamni da for considering service to your country.

The military doesn't care who you are when deciding where to send you. If there is an open slot for someone with your skills in South Korea then they will send you there whether you like it or not. The best you can do is put a South Korean base as your first choice on the "dream sheet" they give you and hope for the best.