Geez, I don't know about that. My band has a tune with a section that is simply Dmin BbMaj7. Over the BbMaj7, I play an e-natural in my line; because the tune is in D natural min (relative minor to FMajor) and the BbMaj7 chord thus functions as the vi chord of Dmin (IV chord of FMajor). That's a practical application of modality. Of course, the general rule of "no natural 4th with a natural 3rd" applies too.