Dissonance isn't relative at all.
Any combination of notes with relation other than tonic-mediant, tonic-dominant, tonic-submediant, tonic-tonic, ie, major and minor (perfect for fifths) thirds, fifths, sixths, and octaves, is considered dissonant. Even perfect fourths are considered dissonant. If you are talking about what SOUNDS dissonant to a particular person, than yes, dissonance can be relative.
Btw - jre58591... I think the pieces you are referring to by the second vianese school sans carter are not dissonant pieces, but atonal pieces. There is an important difference.