There should be a way to make a spawning rule specific to a dimension. END/NETHER biome types suffice for unmodded dimensions, but not the Twilight Forest, the moon, etc.

I asked the same question in IRC and CrazyPants said to add it to GitHub, but you beat me to it.

I agree completely, if we could ban certain dimensions from use by the EnderZoo mobs that would be great

Came here for the same thing. Ender Zoo mobs have taken over the Twilight Forest, when there are supposed to be no mobs at all on the surface there