The b5 is in the chromatic scale along with most other notes

. It's not in the diatonic scales. Also I think the minor 3rd major 3rd play off is more important than the b5th to the blues sound.
I think the minor pentatonic is a great place to start for blues. Once you have that under your fingers, adding maj3rds, b5 and maj6th's is easy. If you learn stuff a step at a time you will absorb it better and be more aware of the harmonic effec the different notes have.
I believe developing a real sense of the underlying chord progression is fundamental to good sounding blues solos. I would rather jam with some one who was playing the changes using only a minor pentatonic than someone who was playing blues scale but wasn't following the chords.