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.