Jon I have winter wheels and tyres for the Polo and A3 (not yet for the Ateca as it's not been a difficult winter and I'd want to see how the 4 drive system copes in snow mode without them first; also not a legal requirement in U.K.). The other cars are FWD hence my logic. In both cases I've fitted genuine OE wheels. The A3 had optional 18' wheels from factory; I've fitted 17's and bigger tyres and it's fine; the Polo has 16' OE winter wheels and tyres.
As Phosphoruc says, the real issues are firstly ensuring the wheel offset is sufficient to give clearance for brake components and doesn't have the wheel coming out from under the wheelarch at all; next is rolling circumference must be with +\- 3 % of the factory wheel &!tyre combo so as not to disrupt speedo & mileage readings.
It is true that any given size of tyre MAY be able to be fitted to slightly different wheels, and vice versa, but that is mainly to do with the tyre cross-sectional width; fit the wrong size tyre & wheel and the tyre risks coming off the rim due to insufficient grip / seating against the rim wall.
Dealers are often not so well clued up; I'd ask a reputable wheel supplier if I were you - but I'd also stick to OE wheels if possible.
Other thoughts - insurance! Assuming you're in U.K. you need to check this for your insurer re. winter tyres (and remember about wheels if you intend to change them too). They vary on notification or not, and in wheels or tyre change only. If you do anything that could be considered by your insurer to present a risk, you could invalidate your cover, so be careful
https://www.abi.org.uk/Insurance-and-savings/Products/Motor-insurance/~/media/4621107A11034C2E98AD503657A699FB.ashx
If you're already aware of any of this, apologies! Info may help others, though
