Some US users say that Metroid Prime 3 is included with a 2.2U update not a 3.0U
(I think its quite reasonable because nintendo didn't even have 3.0U ready when they were makeing the MP3(U) discs)
so if this is true and that you semi-bricked your jap-wii with 2.2J firmware
then you can play
your jap-wii will remain semi-bricked just like before