I've got the same problem. The cause of the issue is that Boot OSX partition must contain a copy of kernel and some additional files all of which are created there during installation. And they are not created if you install Mac OS from the package on installation disk. The partial solution is installing Leopard on raid first then formatiing RAID volume and finally installing SL on it. PCI_EFI will hook up Leo kernel from Boot OSX to load SL from RAID volume.
But this method can cause some troubles too as it involves using an old kernel to boot newer OS. For example some kexts from Extra won't load. And to just replace mach_kernel in Boot OSX with newer version is not an option. I'm working on the possible solution now.
I haven't tried the RAID with Snow yet, waiting on my disc. I was just looking for some updated info on how to do a new RAID with Chameleon RC2. I updated my current config with RC2 manually and it works great.