We're talking about a
server here though. He's not going to use it for everyday activities. Gnome 2 and MATE are just going to pointlessly use resources, even if he has some high-tier specs.
Openbox dependencies. (may differ slightly on CentOS)
MATE dependencies. (may differ slightly)
And if you really need a login manager, LXDM is extremely lightweight and I've never had any issues with it, although an .xinitrc file + the 'startx' command should be enough for Openbox.
Can anyone help set it up?
What specifically do you need set up?