Question about random mob spawning using command blocks.

In vanilla minecraft, is it possible using command blocks to make specified mobs spawn randomly and in random locations throughout a map? for example making ghasts, pigmen, magma cubes, and wither skeletons spawn randomly in a simulated Nether that’s in the over world. And no, I’m not able to just set the biome to Nether because this simulated Nether is located underneath the normal surface in the overworld, and you can’t stack multiple biomes on top of eachother.