No the transaction context is not passed to the downstream orchestration. It is possible that the downstream orchestration will run in another process or even on another server.
The atomic transaction in an orchestration means that orchestration will persist its state at the beginning of the scope and remain active until the scope exits. If the Biztalk process terminates and restarts, the orchestration will restart at the beginning of the atomic scope. There is no mechanism to advise the downstream orchestration that this has happened. If you throw an exception inside the atomic scope there is no rollback, you cannot undo the send if it has completed. You can however add a compensation block to the scope and perform your own logic to undo what may have been done
I think putting a send/receive pair inside an atomic scope will be counter productive. There is no benefit and several possible problems including resending the message.