First I have never used ROS myself, but as far as OpenRB-150 is concerned, there is an example Arduino Sketch named “usb_to_dynamixel.ino” (available after you installed the OpenRB-150 in the regular Arduino IDE of course). Once you compiled and downloaded this sketch to the OpenRB-150, it will act like a “little brother” to the U2D2 but it can only go to 1 Mbps baud rate.
Then you can concentrate on installing and using DXL SDK + ROS on the Pi, which then just sees the OpenRB-150 as another ttyUSB or ttyACM Port.
Recently ROBOTIS released some new version of the DXL SDK for ROS 2