The chain is transmitting the same harmonics a gear drive is.
Chains/Gear drives have been used a hell of a lot longer than belts.
The harmonics of a chain/gear are going to be absorbed by the balancer, right along with the crank harmonics.
If it's a blown motor, the blower belt absorbs the harmonics.
I think a lot of this is more wives tails than truth. If the harmonics were such an issue, you'd see cam bearings trashed on a regular basis.