Watch the Altered Dominant Chords online guitar lesson by Fareed Haque from Jazz Rock Workshop
D7alt= Eb dim and both are almost like Ebmin7. Since Eb dim=Gb dim=A dim=C dim, then we have Ebm, Gbm, Am and Cm almost…and it's the "almost" that's both dangerous and cool. If we use the "almost" tastefully it'll sound "outside," but still cool. If we leave our taste buds at home...well it'll just sound wrong.
Assuming good taste, the 3 pentatonics over Ebm [Eb, Bb, F], over Gbm (Gb, Db, Ab), over Am (Am, Em, Bm) and over Cm (Cm, Gm, Dm) give us all 12 pentatonic scales. So the theory is cool, but when you stand back and look at it all, you might say, "duh, of course you can play anything over any chord, and it'll just sound silly."
The key here is that pentatonic scales have a magic and power all their own. They set up their own feeling of tonic on top of wherever they are. We call this feeling of two tonics - bi-tonality. A lot of amazing music is bi-tonal.
Check out Olivier Messaien, Toru Takemitsu, of course Bartok, Stravinsky, Debussy and many other 20th century classical composers. My opinion is that this music truly rocks, as much as Frank Zappa or Radiohead or Squarepusher (all users of bi-tonality).