So I know I can use legs 1 and 2 (or 2 and 3) as a resistor, but do I need to connect the third leg to ground? It cerainly seems like it wouldn't hurt, but is it necessary?
Nope, don't connect it to ground. It mean you have a short to ground when you turn the pot to the right.
You can leave it unconnected, or connect it to the middle leg.
Connecting it to the middle leg is a standard practice. It prevents the pot from acting as an open circuit in the event of an intermittent contact between the wiper and resistive trace from dirt or wear.
Thanks guys, totally makes sense now. Sorry, I'm a little off my game these days. I think the mental toll of the pandemic is finally starting to get to me.