If they have a Korean keyboard you'll also need to edit your /etc/X11/xorg.conf file. There is a line that reads:
Option "xkblayout" "us"
You can change the us to ko for a Korean keyboard. You can also change it to us,ko to be able to switch between two types of keyboards.
I also don't know which version of VL you are using. Some include Korean fonts by default and others don't. Without those fonts nothing will work. The Hangul fonts you need are in the repository if they aren't already installed.
eMachines EL-1300G desktop, 1.6GHz AMD Athlon 2650e CPU, 4GB RAM, nVidia GeForce 6150 SE video
CentOS 6.5 (will try VL64-7.1 soon)
Toshiba Satellite A135-S4727, Intel Pentium T2080 / 1.73 GHz, 2GB RAM, Intel GMA 950
HP Mini 110 netbook, 1.6GHz Intel Atom CPU, 2GB RAM, Intel 950 video, VL 7.1