While I could see the harmonic issue, I don't think it will be a big deal.
1st. Remember that almost all cars already have a torsion spring between the left and right suspensions. So any issues with cross talk would to some degree be present in conventional systems.

2nd. The spring is a composite. I would assume it has some self damping properties but I have no idea what it's natural frequency is relative to say a metal spring. I'm also not sure what frequency range would be important to consider. For race car dampers the engineers are really concerned with shock velocities around 1"/sec. I assume the natural frequency of any suspension parts would be much higher.

3rd. It has rubber mounts at each end and I think at the points where it mounts to the chassis as well. These would tend to dampen vibrations.