In my setup, COM3 on the PC is connected to the OpenRB-150 USB-C port. Next, the 2XL-430s are daisy-chained into the DXL connectors on the OpenRB-150. Lastly, the other end of the DXL daisy chain is connected to the U2D2 which is then connected to COM15 on my PC.
The picture below is for a WORKING OpenRB-150 via COM3 for Arduino, while Dynamixel Vizard is running via COM15. The DXLs would work in Sync Read/Write as normal as commanded from COM3, and I could see the RED needle on the Wizard’s window moving back and forth too.
But you can also see that Arduino Serial Monitor is picking up MANY incorrect Present Position and Present Velocity values, which are in a way stolen by U2D2 for Dynamixel Wizard 
Next, I unplugged the USB cable from the U2D2 (COM15), which of course froze Dynamixel Wizard App and you can see that correct parameter values are starting to come back to the Arduino Serial Monitor on COM3.
So definitely, on my BAD OpenRB-150 (which was using the same USB COM Port and Cable), the Serial1 and/or the TTL Communication circuitry are not working right. This particular OpenRB-150 is from an older batch which officially has some issues with the FET switch also - see this post below