Out of all the things I've heard about wheels, this is a new one.
Casting/Gravity Flow Forming wheels is nothing new and is really prevalent as manufacturer equipped alloy. The verbage of "Winter Tires Only" really befuddles me as there's really no reason I would see why that might be. If anything, I would imagine it would be the other way around as the cold conditions are more detrimental to a wheel on impact than warm conditions.
That being said, I did a quick investigation to find that these replicas are made my AT Italia from TireRack and they're narrower than the Genuine BMW contours, which would be ideal for winter. Otherwise, I don't see any cause for concern for street use, nor do I see any BMW enthusiasts warning to take heed. In my opinion, I would take the "Winter Tires Only" as a suggestion rather than a limitation. DOT certainly wouldn't approve them for road use if they were unsafe.