What I've discovered:
"Outpost2.exe /loadmod Folder" loads "Folder\op2mod.dll".
"op2mod.dll" should have three exported functions: "mod_init", "mod_run", and "mod_destroy", that are called when OP2 initializes, runs and quits. All functions don't take any parameters and returns nothing (void).
It replaces any OP2's dll that has the same internal name for the one tha is inside the mod's folder.
I know more, but I'm not at home (and my notes are inside my computer)
.