The claim: is just north of Las Vegas on Hwy 604.
What it really is: It's an Air Force that has been around since 1941.
Besides having several major air units, it's other main purposes is for training and testing.
Nellis most likely wouldn't have a FEMA there due to the that fact it would be hard to hide in the first place. Not only is it near the city of Las Vegas, it's also being constantly watch by UFO hunters who think that it is connect to Area 51, so the base is already being constantly watch by people who think that the government is hiding alien spaceships out in the middle of the dessert.