That's assuming only the supernatural side gets to sneak attack. Yes, the nations that dwell in the NeverNever are gonna have an advantage but the ones based in reality have security problems also. We invaded and occupied a foreign nation over 5000 deaths in a terrorist attack. If something like Chicago happened, thre Formor would be seeing some nuclear torpedoes headed their way and most other nations wouldn't bat an eye.
I find it highly unlikely that a nuclear response would be used against the fomor even if their hidden cities were found.
Flooding the deep places of the ocean with Radioactive fallout is a fools game.