I tried running two fans on a “dumb” fan dimmer and they didn’t work very well. On low and medium speed, where the dimmer was limiting the power output, the two fans effectively split the power, meaning that they barely spun at all on low speed, and spun very slowly on medium. I can’t comment on longevity or damage as I only had things wired up like this for a few minutes. I believe this experience would probably be the same with a smart dimmer, so even if the switch and fans can handle it without damage (which I’m not sure about), the behavior of the fans will be undesirable.