The issue with libreoffice not using gtk2 when the gtk2 extension was loaded, except after loading gdk-pixbuf2.tcz, was a problem in the gdk-pixbuf build in gtk2.scm. It needed --with-x11, so I built gtk2 self contained in libreoffice and now the gtk2 toolkit works, and without needing gtk2.scm.
I will also fix the gdk-pixbuf2 build in the gtk2.scm extension.