Hmm, there is still one problem I can think of, which I once suffered myself:
I once installed Dom2 on my Linux machine globally as root. Forgot about it (because of non-functional OpenGL drivers at that time - never ATI-grahpics for a Linux Laptops again
) and installed it later on again locally.
Afterwards mods would not be recognized, since I was installing them in my local installation while entering dom2 on the commandline would run the global installtion, which thus missed the new files...
So do other mods work for you or is it just a problem with oceania? What is the version shown in the main menu?