How has this seemingly impossible task been achieved? Seasoned Mac enthusiasts will remember the days when Apple machines used PowerPC processors, and the Wii uses a PowerPC chip thats a close cousin of those used in the Mac G3 series of computers. Since the Wii can run a Linux-based OS, it can therefore run Mac-on-Linux, providing in theory an environment in which it can host one of the PowerPC versions of MacOS.
Source: Its MacOS. On An Unmodified Wii!
Huh, look at that