There’s always a risk when you buy a used car - nearly new or otherwise - that the wheels may have been refurbished. White worm corrosion would be covered under VW’s new car factory warranty if the white worm was the result of a manufacturing defect. However, if the wheels have been refurbished, then VW won’t want to know, as the white worm may be the consequence of a poor, substandard refurbishment. Similarly, if it’s the result of stone chip damage, VW wont entertain a warranty claim - they’ll maintain the damage is the result of an external influence. The dealer you bought the car from may be willing to submit a warranty claim to VW. However, as above, if the wheels have been refurbished or have / have had stone chip damage, then unfortunately I don’t think you’ll get anywhere. No harm in asking them though; if you don’t ask, you don’t get.
I’m not a fan of diamond cut alloys to put it mildly. The diamond cut lacquered finish isn’t very durable compared to a painted / powder coated finish especially when subjected to winter road conditions, and lots of diamond cut wheels succumb to white worm when they’re around 2-3 years old. I’ve currently got them on my car but hopefully not for much longer - I’m planning on replacing them with a set of more durable painted / powder coated wheels.
Good luck if you do decide revisit the original dealer. Please keep the forum updated on developments.