When you generate a MAP with parameter "use RSO biter generation" off it makes no biter nest to spawn at all.
If it's working at intended at least there should be a message stating that.

It is working as intended with small difference.
There is a second setting in startup section that you can use to enable vanilla generation.
By default vanilla is disabled and RSO is enabled.
I'm not sure if it needs to have a message tbh - it's named RSO biter generation so when disabled biters don't generate. I'm not sure what else could be added in explanation.