Does the ADSB system interogate normal Transponders as well?
AFAIK, Yes and No, an ADS-B ground unit only receives information; but it does send a signal to say I'm here, how about you. This is on 1090 the same as Mode S.
The Flashing R (assuming regular non mode S - transponder) is more likely to be TCAS interrogation from those above.
Plazbot, stop encouraging the terry towelled hat wearing flat earth society.