Seoul is a big city with a population similar to that of New York. It's an ugly city made of concrete and brick. There are older parts and newer parts. I have never seen what could be considered a ghetto in Seoul. Most are older and usually suffer from some type of obvious medical problem, such as blindness, missing limbs, etc.
Blind people begging on the subway trains are a common sight.
I do remember seeing two young girls begging alone on a subway train. They were obviously sisters. The older was maybe nine or ten and other about six years old. They were both dressed in dirty clothes and unwashed, which is extraordinary for the usually immaculate Koreans. But this was the exception, not the rule.