Theoretically, absolutely. Passengers transferring from a one-world J class flight to a domestic segment in Y should have J lounge access on that basis. In practice, I don't know anyone who has done this on a BA-AA connection at JFK, but it definitely works for AA-BA connections at LHR. Seeing as the Dragons at Terraces are usually tougher on credentials than the AAngels at the Admirals Clubs, I would be surprised if you have a problem.
If it is you who are travelling, you should also have access on the basis of being BAEC Silver (OW sapphire) regardless of class of travel. All non-AA Sapphires get AC access when travelling on AA, regardless of route or travel class.
Thanks, I am travelling with the wife & kids who are blue. We are on redemption flights including Club on BA to JFK and AA First down to MCO, doubt we will have time for much in the airport but its always nice to be able to chill out between flights. We will give it a try and see what happens!
