I have successfully done this (i.e. placing the widgets, not skinning them) with gnome 1 and sawfish (`crux' theme). I haven't tried w. gnome2 & sawfish--and I can't seem to find the `theme options' w. gnome2/metacity/crux;
So, it *can* be done w. gnome, but I think it's wm specific.
In any case, good luck, and sorry for not being more helpful