Sensible answer (For once)
The windmills will give false velocity returns on a pulse-doppler radar (As carried on F15, F16, F3, F18, F4 but not GR4). I've actually locked to the velocity generated on helicopter rotors before (Who said hovering hid you guys!!), so I guess this is the same.
BUT it won't jam or deceive radar just create velocity targets where the windmills are situated - no big deal, I guess.
I hope this answers your Q, LJ.