I've been hoping that PearPC would add support for open BIOS so that I could test MorphOS with this PPC emulator, but sadly this hasn't been added, and the emulator doesn't seem to have been worked on for a long time now.
There are a couple of other PPC emulators. PSIM is now very old (1996) but I've heard it still works well for a lot of PPC emulation. And Qemu which is the newest and most promising. I've not tried either but am interested to see if either could be used to run MorphOS. I will have to investigate.