I am not sure what the RAF Official regulations says about "crew victories". However, in spite of the air gunner taking aim and firing the guns, often one depended of crew coordination and cooperation to achieve such a claim (the pilot, in most of cases needed to manoeuver the airplane, either avoiding an attack or looking for a favourable position for his gunners to shoot). Radio-telephony was paramount on most of those claims, I believe (and have read about).
It is strange that Keys' name is not recorded here:
http://aces.safarikovi.org/victories...th-gunner.html