US troops have been ON the border between North and South Korea since 1953. The US is actually talking about pulling about 12,000 troops OUT of South Korea (of the 37,000 who are stationed there).

I don't know if ROK (Republic of Korea, the south) troops are in Iraq. I wouldn't be surprised, though. I doubt that they are converting to Islam -- Koreans are Buddhists, animists, and Christians, mostly.

That said, the ROK army is one of the toughest and meanest in the world. They are well trained, well equipped, and quite ready to fight. Their record in Vietnam was outstanding -- and they had no qualms about committing what we would call "abuse" to obtain information from prisoners. (This does not mean I approve of such.)