Best of luck.
Certainly, the existence of the system should be disclosed. Meanwhile, if the amount of electricity being used is insignificant, don't be shy about pointing out this fact. Actually, you could demonstrate it by showing prospects the electric bills for the past year.
My advice: If a potential buyer is "put off" by the Radon situation, smile and let them go. They'd probably find a half-dozen OTHER things to grumble about, also. [Grin.]