Recently, xlockmore stopped using it's config (resource file in /etc/X11/app-defaults/XLock). I didn't notice when this has happened, but IIRC this happened after I've upgraded to modular X, not when I upgraded xlockmore (downgrading xlockmore didn't help). I did strace xlock and found the problem - xlock tries to load it's resources from /usr/lib/X11/app-defaults/XLock. My /usr/lib/X11 didn't have an app-defaults directory. I did "ln -s /etc/X11/app-defaults /usr/lib/X11", and xlock is now working properly. My guess is modular X distribution doesn't create this symlink, while the monolithic X did. Not sure, though.
There does seem to be some confusion about where an app should put it's defaults and where it should look for them. See also bug 107431, which suggests it should really install in /usr/share/X11/app-defaults, but should also read /etc/X11/app-defaults for system overrides.
This is still an issue. I've done a fresh gentoo install on another computer, and I don't have a /usr/lib/X11/app-defaults symlink to /etc/X11/app-defaults. Had to make it by hand to make xlock read it's resources.
Should be fixed in xlockmore-5.23 now, using /usr/share/X11/app-defaults
