Hello,
I'm writing the following assuming that we're talking about a V/Oct pitch CV.
You wouldn't be able to quantize the Mimetic Digitalis's CV without a quantizer. By offsetting MD's output with Voltage Block's output, you are doing just that: offsetting MD's unquantized output with VB's output. This would not quantize MD's output.
You're second idea will work though. Since VB's sequence is already quantized, you can offset/transpose that sequence with MD's output. So the melody is coming from VB, and MD is transposing it up and down. If this is what you want to do, then @farkas is right, you will want a precision adder.
I hope that helps, and I'd be happy to answer any further questions if I'm able to.
-Chace