Solution: Run OOo with environment variables set as:
OOO_FORCE_DESKTOP=gnome
Note: In KDE variable value should be changed to 'kde' instead of 'gnome'.
Packages like openoffice.org-[gnome/kde/gtk] need to be added for this feature to work in some linux distro's.
gtk-chteme package is also a good choice for changing GTK themes apart from Gnome Control Center.
Ext. links: Environment variables in OpenOffice wiki
See also: Archlinux wiki on substituting fonts (this might be useful for improving OOo interface fonts, which are Sans by default)
