I am a keyboard player and as an exercise, I like to figure out riffs or background chords to songs I like and improvise over them. I chose to tackle this riff, starting at 6:14 with a guitar soloing at 6:42. I have transcribed my best guess at the piano in the background here, but due to my limited ear training this may be incorrect.
From what I hear it sounds as if the scale being used is natural minor, however if so, I don't see how it would work. The minor scale, I believe, would work fine over the dominant chord outlined by the first four eighth notes, but not the next six, which I see as fitting in Lydian dominant.
If the scale being used is minor, could someone explain why it works so well? Also, regardless of what scale is being played in the actual recording, I would like to know what other scale I could use. I have tried various dominant scales, but the only other scale I've gotten to not sound too "outside" is Dorian. Also, if my transcription of the riff was off to begin with, please let me know and I can reevaluate.