When I connect the gimbal to the camera (via the supplied cable), I lose connection to the external monitor (iPhone connected via wireless from 5d mounted on gimbal).
I haven't been able to find any references to this online - so I'm thinking it might be something I'm doing incorrectly.

Is it possible to be simultaneously connected to the monitor, while the camera is physically plugged into the gimbal? Manual focus using the gimbal focus wheel is nigh on impossible otherwise.

Thanks in advance for any advice here.

On page W-14 at the back of the 5DMk4 manual, there is a note under Interface Cable Connection Cautions:

During a wireless LAN connection, you cannot use the camera by connecting it to Connect Station, a computer, a wireless file transmitter, or another device with a cable. Terminate the connection before connecting a cable.

So, this doesn't appear possible.