Why would it be emulated? This is OS4 for CLASSIC, i.e. amigas that have a 68k cpu. In fact since it's for CLASSIC and requires a PPC chip there must be a 68040 or 68060 on board the PPC accelerator as well.
No, the 68k cpu IS emulated. I think they said something about "turning off" the 68k, as it made the PPC even faster. I'm not sure about the technical details though.
--EDIT: I've been informed on IRC that this is actually quite silly. I think the quote I half remembered was actually referring to the lack of context switches between 68k and PPC.
But the 68k emulation is reportedly very fast. Usually faster than an 060 on a CSPPC.. (of course speed will vary between different applications).