I wonder why? Has anyone tried running the JPN version, let it do its updates (safe on your JPN Wii) and then try running the US version (brickblocked)?
even if you update with the jpn version, it will still be the same firmware after the update(i'm grabbing the jpn spg because I semi-bricked my fw 2,2J wii with big brain academy us and want to unbrick it). unfortunately, it won't ameliorates the odds of being able to play the us version of smg.
the same situation happened with big brain academy us, even if you put brick blocker on the iso, it won't work. that's the price to pay for having a console that is not in the same region than the one of the game.