xemacs can be compiled with --with-site-lisp. Some rpm-packages like a2ps,
gnome-libs-devel and gettext are placing files into
/usr/share/emacs/site-lisp. If the site-lispdir will be set to this
location some files can be shared between the two emacs's.
I don't think this is a good idea, as the byte compiled lisp isn't compatible.