While he will certainly be able to access the NRT T2 Admirals Club based on intl class-of-service + onward oneworld flight according to the section of AA's lounge access rules cited by gemac, I'd be careful about making a blanket statement with respect to other oneworld airlines' lounges, particularly JAL.

JAL explicitly restricts COS-based access to those departing on JAL Group flights. While it's true that he is departing on a JAL Group flight from NRT, the COS is from the inbound AA flight, which JAL may or may not recognize as qualifying for access. Certain JAL economy fares do qualify however:

http://www.jal.co.jp/en/inter/lounge/member/class.html

We've touched on the distinctions between status-based and COS-based access, and the vagueness of the oneworld rules for the latter, recently here and over on TB. Bottom line, NRT AC is a safe bet; JL may be worth a shot, but don't be surprised if the answer is 'no'.