Hi,
I have the Nvidia Shield, just purchased it as didn't want the expense of a new iPad Air which doesn't fit in flight box.
I have tried the gimbal operation in slave mode, but it does work fine in master mode, obviously only controlling up and down movement. There is no reason why in slave mode you shouldn't be able to fully control gimbal as design. Also on a side note, i've seen somewhere online, youtube, that you can control gimbal in any direction using your finger on the screen whilst flying in Master mode, but haven't yet had a chance to try.
I can say however, I have experienced a small amount of lag using Shield, say approx 1/8-1/4 sec, but have since changed std settings on shield to work in performance mode when using DJI Flight App, as you can control how the shield distributes its processing power manually app by app.
Chris