Since SN Sabena is no longer part of OneWorld your status will not get you into the club with them. And you are flying coach so again.. no club.
As mentioned the BA lounge is in the International wing and technically you need to be flying a OneWorld carrier that day to use that lounge. You would be able to use this lounge on the RETURN BRU to JFK but probably not on the origination...(with your PLT status)
The BRU domestic side is totally apart from the international and once you get there you cannot return! I was stranded by a SN (old SN) strike and had no way for AA to help me change my flight as I was stranded in the domestic portion of the airport.