From my PowerBook/iBook experience, I can run OS9 and many of its apps (FreeHand is a must for me) on top of OSX on my PowerBook G4 BUT I can not select it on my boot options. However I can select OSX / OS9 as boot options on my G4 iBooks. On both machine sets (I have a few iBooks and PowerBooks) the Classic system Panel icon is there.

Never understood why.

Edit Addition: On my G5 Tower (2.1GHz), OS9 also works on top of OSX, but I never tried to boot it up from OS9. Talk about wickedly fast!