@Caesars_Palace,

I would highly recommend finding a plastic switch plate cover, since most boxes use a standard sizing. While everything is grounded inside of the electrical box, using a metal cover will still introduce more risk to the device. 

More importantly, using a metal plate cover will likely create a cage for the Wi-Fi signals of the switch. I could definitely foresee problems with your device maintaining its connection to the network or being quick to respond to cloud actions.