While Coppermine supports already a good number of files, allowing kmz-files could increase its potential even more.
There's a workaround offering them as a zip file but it's more member focused not to.
just add those files to the filetypes table, see http://forum.coppermine-gallery.net/index.php?topic=18012.0
However, this should have been asked on the support board that corresponds to your coppermine version, not in feature requests.