The mod provides scaling culture, much like how libraries provide scaling science in the base game. If you have 1 population, a monument (2 per 5) will produce 0.4 culture. If you have 10 population, you get 4 culture. I put all scaling to "per 5 population" so whole numbers would be used, but it does keep track of fractional amounts if you have some non-multiple of 5 population.
As for Oligarchy, this mod should have no effect on that. I've never really tested it. And as I understand there's still quite a few bugs in the civics code at the moment. Like if you switch from one incompatible civic to another, you get all of the "one time" bonuses again. This is a problem that needs to be fixed in the base game.