Actually SRV uses the blues scale and the shadow pent in alot of songs. He uses other tricks to but this is a signature SRV move. So for example If the song is in Amajor He would play the blues scale. This is basically the #1 Pentatonic (w/blues notes) played starting on the 5th fret A. He would also mix in the #1 pentatonic scale starting on the second fret. It's a little tricky to go back and forth between the 2 with style but that is the simplified idea behind the shadow blues. This can only be done if the song is in a major key though. And it works for all 5 parts of the pentatonic scale.

Hope that's clear.