> Would a SCSI card that works in the Pegasos II work in a Power mac?
> I remember some comments about having to flash cards for Mac but
> I don't remember if that was just video cards or all.

A PPC/OF ROM for the card is necessary if you want to put the MorphOS boot.img on a storage medium connected to the card. Without PPC/OF ROM, you can still put the MorphOS system files on a storage medium connected to the card as long as the boot.img (which has to be loaded from a different medium then) has a driver for the chipset of the card, which is the case for the SCSI chipsets mentioned in comment #2.
And of course, that card must comply with the PowerMac G5's PCI specs. The Pegasos' PCI slots are 5V, while the PowerMac G5's PCI slots are 3.3V, so only 3.3/5V-dualcoded cards are compatible with both. Incompatible cards won't fit physically.