Mods beside Heroes or CB Mod (or a few others) are only useable for singleplayer.
In multiplayer its really difficult to build in nation mods. Maybe you can start an only-mod-nation game but only allow one player to get a specific mod nation doesn't seem to work. You still have the ballance problem here.
And because i hate playing Dom3 SP games i only test some nation mods for 2-3 turns and so mainly don't use mods (besides the MP mods) really much
