So, since updating to Dalek Mod Update 64.1, hostile mobs from vanilla Minecraft have stopped spawning entirely making progression in survival mode impossible as both Endermen and Ghasts are no longer spawning in my world.

Did you re-download the mod? Cause SWDteam told us to download update 64 again, cause John uploaded an older version of it. And it has loads of bugs

They said it was update 64.1 in the title, that's the right one

Maybe Dalek Mod mobs are pushing hostile mobs out. You can try disabling invasions and lowering the spawn rate or removing overworld biomes from their spawn points. These two files can be found in the .minecraft/config folder