The health risks are mostly conjecture. First, no one has proven that EMFs cause cancer. EMFs might. It's possible, but no one is really sure. Furthermore, even if some EMFs caused cancer, you'd then have to prove that the EMFs in hybrids and in electric cars cause cancer. Some people might be sensitive to EMFs, but that is an unknown factor as well. For safety's sake, pregnant women may want to consult a doctor before driving a hybrid or an electric car.
The only real health risk is crashing your car, but you don't need an electric car to do that.