Yes, you can get harmonies that are not quantized by adjusting the cents parameters for a given voice rather than setting the interval. For example, raising a voice by 300 cents will give you a fixed minor third that will not be quantized to the scale setting.
Page 5 of the user manual has a cents-to interval conversion chart: https://downloads.eventide.com/audio/manuals/plug-ins/Quadravox+User+Guide.pdf
-Tyler
