The difference in oil viscosity isn't going to make any real difference in the sump bulk temperature (probably less than a few deg F) that would effect fuel dilution burn-off.One simple thing that could be helping , that has zero to do with the Brand oil in the sump is maybe the 0w30 is helping the engine heat up faster, resulting in less fuel making it and staying in the oil. Of course not a miracle "fix." There is none for a 100% known design flaw that the manufacturer refuses to admit to. Yet at this point, anything is helpful since the wife loves her car so much, dilution or no dilution.
Stuck rings could certainly increase combustion blow-by and therefore the level of fuel dilution. Having clean and 100% free rings to seal properly is pretty important to the performance of the engine. Anything to help keep them clean and free is a good thing.