Most Definately the Referee can bring percieved foul play to the attention of the TMO to have a look and suggest correct sanction. In this instance, as we know, this is useless as none of the officials saw anything. »
If you listen carefully, just before the Saracens player rightly points out he has been smashed, the ref says "Robin", most likely a question to the closest AR to ask if he has seen anything. given the lack of response, the ref had no option but to play on if he hadn't seen anything. »