I solved the problem. If you get a 'Cannot Process Raster' errors, the Z600 raster filter cannot read the required datafiles. When converting the RPMs and installing the resulting tarball or deb package, certain directories end up being readable only to root.
To check if this is the problem, try and look at the /usr/local/z600llpddk/utility/ directory (with ls or with your favourite file manager). If you get a permission denied error, chances are the conversion filter cannot read it either.
The following two commands will fix this for you. Run these as root (sudo or log in as root) to fix this, and another directory likely to have the wrong permissions:
These changes made the printer work for me.
chmod -R +rX /usr/local/z600llpddk/
chmod -R +rX /usr/include/lexmark/