Well, hold on there. Halfling and gnome-ruled polities may not be around in the Greyhawk material, but that doesn't mean there's no room in Gygax's Greyhawk. If you look at the setting as published in the 1983 boxed set, when the various polities refer to demihumans in significant numbers to call out specific varieties, halflings and gnomes come up a lot and spread widely. They may not be the high and mighty NPCs, but there's plenty of room for their involvement, their presence in the background, and halfling/gnome PCs to come from just about anywhere.