It seems like you got this issue resolved. Did you manage to successfully communicate between the bluz DK and the ReadBear Duo? I'm in much the same position as you were some months ago -- I have a RedBear Duo and a Bluz DK, and I'm trying to get the Bluz to send data to the Duo using BLE.sendData().
I have the functionality working on the Bluz gateway, which is forwarding BLE data correctly, but I want to replace the gateway with the Duo. I'm currently modifying the Duo example code in "simple central", but haven't managed to successfully read a characteristic. Any help you can give if you've solved this problem would be most gratefully received.