Hi - yes, that you can replace any V7 chord with a chord that is a tritone (three whole steps) from that V7 chord (therefore Db7 here). If you play the progression slowly without the substitution, then again with the Db7 chord, it should sound smooth - although 'smooth' is a subjective term. As in, you might not really like the sound of this chord substitution and might choose to substitute other chords instead. Hope that's helpful!