I ran a similiar fogger system as you describe.
If you use a fan to circulate the fog without a return system, the fog must go somewhere. It will creep upwards through your medium and your stems can become too wet, soggy, fungus, weak. etc.
Also, the ultrasonic foggers increase even large res temperature way too high! You will need a chiller to continue this system. Seems to work with clones without a chiller, as they like warmer roots, though