When using SWD interface, is the reset pin necessary?
Yes, eventhough the name is Single Wire Debug, you will usually need 4 connections:


SWDIO (to transmit data from the programmer to the target)
SWDCLK (to clock the data that is being transmited)
RST (to perform a reset of the target)
GND (for the signals to be referenced to something)


The reset is kind of optionnal if you are willing to press a reset button manually if the target get stuck/freezes.