I plan to use a battery which is going to a 5V BEC to supply the power.
Question 1:
Is it possible to supply power via the 3.5mm screw terminal input (as shown in the “External/Battery Power (Better)” section) when it is docked to an Arduino Uno?
Is it possible to supply power via the 3.5mm screw terminal input (as shown in the “External/Battery Power (Better)” section) when it is docked to an Arduino Uno?
yes.
Question 2:
Will that feed power into the Uno as well?
yes,
On the NanoM6E board is a diode to allow the power to flow from the battery onto the board. As such the power on the board is 5v -~ 0.7 (diode) = 4.3V.