To use a vanilla Kingdoms example, York_Province is assigned to these factions: england normans denmark scotland hre saxons france.
York starts as slave. The developers knew this and the game does too. So to put York_Province in this pool was incorrect (as are other examples) if this file does mean "starting owner" .... which I strongly suspect it does not.
dominant culture: by that you mean "religion". Yes it's possible but I doubt it: why bother making the modder list factions instead of religions directly?