This vibrato that I call the "open hand" vibrato, IS what it's called. You're using a open hand around the neck, to facilitate greater, quicker, and more aggressive movement of the fingers and hand, and thus increasing the impact of the vibrato. This type of vibrato is most often seen (and heard of course) amongst texas blues players, but can benefit you greatly when you want to make an impact in any musical scenario.
Check out the video for details!