Yes, GNOME resides on the file system, so you can install it to your SD card assuming you let the kernel know it's the root file system or mount the proper places from the file system.
More info on installing GNOME:
http://lfs.osuosl.org/blfs/view/svn/gnome/gnome.htmlI haven't tried this yet, so this is about all the help I can give you.