I have not heard about cases of erectile dysfunction after kidney donation, but somewhere from 5 to 10 percent of male donors suffer temporary or long-term pain in the testicle on the side of donation, and it seems to be caused by problems with the blood supply to that testicle as a result of the surgery.
You might wish to also post your question at the FaceBook page of Living Donors on Line as there are more donors who check in there who do not check in here.
Fr. Pat