Answered my own question is evening at BWI. Hopefully this thread will live on in the archives to answer someone else's question.
bA lounge is called the "chesapeake club" and is near the entrance and exit of concourse E (international). According to the resident dragon - who lived up to the moniker - only BA first and business class customers (plus their equivalent of Es and SEs) are allowed in. Paid access is also not permitted.