I can't seem to find any mobs from grimoire of gaia or elemental creepers redux spawning in the overworld. Might be several other mods that add mobs that doesnt show up. Is this a normal behaviour? They seem to spawn properly with biomes o' plenty world gen.

Realistic gen uses vanilla generation so shouldn't be Quark's fault.

Oh that's right. I'm using other major biome adding mods like traverse and novam Terram along with quark's realistic Gen. Those might be the one causing this to happen.