Quick update.
The module doesn't build if dkms is invoked via
dpkg-reconfigure fglrx-modules-dkms.
If dkms is invoked directly then the module is built and installed correctly
dkms build -m fglrx -v 10-4 -k 2.6.32-5-amd64
dkms install -m fglrx -v 10-4 -k 2.6.32-5-amd64