I truly have no idea if the PPC can actually directly respond to such an interrupt if it does show up.
How it is possible to run Linux, MorphOS, AmigaOS4 and many many more on those boards?

Do they have secret 68k interrupt handler or something? ;-)
Worst case scenario is that the interrupt would be handled by a 68K task that can wake the PPC, but I don't really want anything that requires an 800 microsecond round trip for something fairly time critical
You are out of luck I'm afraid.