Assuming that the leaked map is real, my guess is that the snow and ice in the snowy neighbourhood will be just a white ground texture that can't be interacted with, at least not in the same way as the snow from Seasons. The pack will come with its own snow-related activities instead. And even if they do copy and paste some of the Seasons activities (such as building a snowman or having a snowball fight), it will only be possible in that one neighbourhood that has permament snow. It would be weird not to have any temperature effects there, but this is TS4, so who knows.
For people who do have Seasons, I suppose even the greener neighbourhoods will be cold and snowy throughout most of the year, except maybe summer.
