FWIW I have yet to run into an intel machine that won't boot off the Service Leopard partition. It's possible that the firmware in even the newest machines is OK with Leopard.
It should be noted however that I did have to reinstall Leopard from a Mac Pro image when the newer mac pro was swapped in over here, it would KP if I booted off my service leopard. I didn't spend the time to track down why, but I assume I'd have seen a "no drivers for supported platform xxxx" message in verbose indicating it did not find a driver for a critical bit of hardware. (such as CPU, usb bus, etc)
Leopard and Snow Leopard are very very similar.
