Well... it depends.
There are
three (mtb) displays out there
- SC-MT800 (with BluetoothLE / ANT)
- SC-M9051 (with BluetoothLE / ANT)
- SC-M9050 (without any wireless connectivity)
Shimano does indeed state that you can have a maximum of one wireless capable unit installed.
If the M9050 is installed on your bike then I would expect everything to work just fine.
Even if you have one of the other units, I'm not sure what would happen if BLE / ANT were disabled on one of the units.. The system may still function.. I have never tried

.. I do have an SC-MT800 and EW-WU111 here, so maybe I will try that soon..