As requested, My winter rides in Colorado on my IGH have proven no different than summer rides.
I don't notice any more drag, yet my 12.5 mile commute always takes longer in the cold so maybe it is the hub. (I rather doubt it.)

I park my bike indoors on both ends of my commute so perhaps it has a chance to dry out before freezing up?

I find I have far fewer winter commute issues with the IGH hub than I did with conventional 3x6 (older bikes) drivetrains.