There is a port of UAE and another Amiga emulator for the Wii.
Someone should start a bounty for an AROS port.
Rogue has stated that the Wii is capable of running OS4...
But since you bought a new Wii, it is not soft-moddable currently...I think. Perhaps through the IndianaPWNS exploit it might be though. Whatever you do, do not upgrade to System Menu 4.2 as that removes homebrew.