No, not really. Each toolkit has it's own settings. You've aparently set the QT options, but GTK applications will ignore that. Use Nautilus to get to the Gnome2 control center and you can set fonts for GTK2 apps there.
Fonts for GTK1.2 apps have to be set with a gtkrc file, you can probably use the theme-switcher (non gnome app) for that.
This of course doesn't affect programs that use other toolkits, such as xaw, tk/tcl, motif, lestif, wings, etc.
Unfotunately fonts in X has always been a pain.