It's going to cause an issue eventually if/ when 1 tank runs low enough to lose prime and siphon effect. NBD I just don't want to be the guy adding fuel to the low tank at the side of the road.
^^^ This
If the system would work well without a selector valve GM wouldn’t have spent the money putting them in.
If you need to hack it to get by for a while, then so be it.
Whichever tank has less resistance to pull the fuel from may end up getting ran dry faster than the other. When my selector valve went bad it pulled from both tanks, too many times one tank would run dry and would not even be able to start unless I primed the carburetor even after adding gas to the empty tank.
You’re better off replacing or repairing the selector valve (common failure), switch, or wiring.