They are all rangers. New California Rangers. Do you mean the desert ranger? The guy with the trench coat and gas mask?
No they're not.
The NCR is the New Californian Republic. They're all Californians.
The NCR Rangers are modelled on the Texas Rangers. They're the NCR's only known elite military force. They're multiracial, and have a chip on their shoulder about slavers.
http://fallout.wikia.com/wiki/New_California_Rangers
Edit: Rangers are confirmed
http://fallout.wikia.com/wiki/Ranger_Ghost