A metacity theme defines a style_set for each of the "normal", "dialog", "modal_dialog", "utility", "menu", and "border" kind of window. With Compiz enabled, the "normal" style_set is used for all kinds of windows, and the window decorations aren't even drawn for detached menus ("menu" kind, in Gimp for example).

I'm using Gnome on Mandriva 2008.0.
$ rpm -qa | grep -v devel | grep -E 'xorg|compiz|metacity' | sort
compiz-0.5.2-9mdv2008.0
compiz-decorator-gtk-0.5.2-9mdv2008.0
compiz-decorator-kde-0.5.2-9mdv2008.0
compiz-fusion-0.0.1-0.3mdv2008.0
compiz-fusion-plugins-extra-0.5.2-4mdv2008.0
compiz-fusion-plugins-main-0.5.2-4mdv2008.0
libcompiz0-0.5.2-9mdv2008.0
libcompizconfig0-0.5.2-2mdv2008.0
libcompizconfig-python-0.5.2-1mdv2008.0
libmetacity-private0-2.20.0-1mdv2008.0
metacity-2.20.0-1mdv2008.0
x11-server-xorg-1.3.0.0-24.1mdv2008.0