Well, Ubuntu's utilities can partition a pendrive using GPT, so this part souldn't be a problem.
I guess there's also a way to "restore" partition from ISO file, so you could get a DMG image of Snow Leopard disc, convert it to ISO and then restore usb partition. Installing chameleon from unix based system shouldn't be much of a problem either.

But if I were you, I would first try other Leopard distro eg. iDeneb 10.5.8 Lite

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AMD Phenom II x4 810 2.6GHz | Gigabyte GA-MA790XT-UD4P | Gainward GeForce 9800GT 1GB | 6 GB 1333MHz DDR3 RAM | 1TB HDD | 19'' Widescreen Samsung LCD Display
Mac OS X Snow Leopard 10.6.4 (Everything works except Safe Sleep) | Windows 7 Home Premium x64