I ended up trying it. It does work on Snow Leopard, at least on my machine. Keep in mind, you will need to have Rosetta installed to run it, though the system should give you the option to download it if you try to open MacDraw without having it installed. However, MacDraw can't display anything within a document when it saves a file. Curiously, saving the file as a PICT saves the drawing/text/whathaveyou but doesn't display the document background at all, according to Preview running in 32-bit mode.
After using MacDraw, I can see that the Finder would be only a curious little toy, since it only has access to the bundle's system folder and to the Documents folder. I don't see any reason why Desk Accessories and Extensions, even Control Panels, wouldn't work, at least from an architectural perspective, since the bundle has a Finder binary and a System file. That said, we'd need a port of the Font/DA Mover to use Desk Accessories, and this version of Font/DA Mover would have to be able to install into the System file of every GrayBox bundle. I would like to see Color QuickDraw support and feature parity with System 7 and Mac OS 8 (since I jumped in during that era), but it beats starting up an emulator each time. Also beats the annoying process of trying to find ROMs and disk images.
I downloaded the source (which was a pain to figure out how to do) with the intent of messing around with it, but it requires Metrowerks CodeWarrior, which means I'd have to switch over to my iBook to work on it, since all I've got on my MacBook is XCode.