I've some analysis in Darkmatter.
It's not much, only a little header information.
It seems to be encrypted.
There is an array in the begining of each vertex chunk ,i'm guessing it's kind of coding table.
here are 2 samples,,one is dumped from emulator,the other is extracted by off-zip.(you can find offzip in Xentax)
Sorry for typing english here,I've no confidence with my japenese grammer :P
Thank you for your reading,please help if you have some idea about it's encryption method.