Keep in mind that you can’t just put a ‘dimmer’ on a regular oscillating fan, not unless you want to kill it and/or cause a major fire hazard. Avoid that approach, even if you find lots of DIY projects doing it this way. It’s dangerous.
But it should be possible to create a simple Raspberry PI controller with the ANT+ USB module or one of the Zigbee/XBee modules to work with that to power and modulate fans in a way that simulates real-world conditions.
The trick is not to get Zwift to control the fans, but to get your bike’s own sensors to control the fans. ANT+ is already on the bike, and sending data about power, cadence, speed… so parsing that (as Zwift already does) could also be parsed by the Raspberry PI to turn up the fans (higher speed detected) or turn them down (lower speed detected).