Do air ionizer harm electronics?
I'd be concerned having one of those too close to my electronics for an entirely different reason.

I used to have a couple of those and they worked ok but after a number of months I found that the walls and other objects within a meter or so were accumulating large amounts of dirt. Charge build up on the walls was attracting almost as much stuff as the receiver in the cleaner. Since we smoked at that time, the build up was a mess.

Having that kind of accumulation inside your circuits would be a bad thing.

As for ESD. If your electronics is grounded, charges should not build up on the circuitry itself. If the air is ionised enough any charges built up on plastic parts will leak away to the grounded circuitry. If no grounding exists however, static can build up on the entire unit though discharge strength should be reduced in the ionised air.