I do not understand the logic behind which ones work and which ones do not. Nether works, but End and Twilight Forest (ID 7) don't.

Ok, so the End does work if set to use dimensions of type ENDER, which currently is only the End because no other dimensions other than vanilla use types properly in 1.7.10, it seems.

Twilight Forest has no such category that I can use.

It's even stranger because when using the ID 7, it shows green, meaning it should work.