Rotor downwash on a gyro is very dangerous as it relies completely on the rotor being in an autorotative state. If the airflow gets reversed, the rotor stops flying. At least one crash is accounted to this. Helicopters have this same problem, but most of them can power out of it (most of the time).
I have not encountered rotor vortices when flying FW, but I can imagine they could be rather hairy given the right circumstances.