I can confirm that 245/45R18 tires fits and run perfectly fine on 18x8.5 wheels.
The other questions is which Yokohama Ice Guard tire model are you being offered?
Ice Guard is a sub-brand, and there are multiple models within it: IG51, IG52, IG53, etc.
Ice Guard's are an OK winter tire.
I wouldn't recommend buying it, but if you get it for free, then it's better than an all-season donut: