Like the title says, Is it OK to powder coat the Harmonic Balancer? I am asking because of the rubber.
Thank you.

no. powder coat oven temps are too hot

I wouldn't used to design dampers for Schwitzer would compromise the rubber

That is what I was afraid of.
Now I'm questioning the idea of powder coating the flywheel cover as it has rubber bushings also.

No either but it can be a good thing for your pulley's if they get rusted up. The rust in the pulley grooves can wear belts in no time. Some Volvo Penta's have this problem badly and snap V belts - not good when it takes out the v belt for the impeller housing. just throwing it out there.

I would use some good epoxy paint such as KBS-Coatings.com

They use plastic and rubber plugs to plug threads, etc. when they powder coat and they live.
Smoke comes off my rear tires on occasion and the tires aren't compromised.
In theory you could probably do it.
But I wouldn't. lol