I guess it depends where you live. I've never seen any water at all in my window well, even after heavy rains. Anyway, if there had been a flood, the water would have been pouring in through my window screen (I use this to ventilate my crawlspace), way before going through the dryer vent (the vent is about 2 feet above the floor of the window well). At my sister's house, however, her window wells have been flooded a couple of times in the past 10 years, so I may not have used the same solution for her house.
Concerning the snow, because the well is quite deep and near the house, it is very rare that it gets filled with snow (and we get plenty of snow here up north). Maybe once or twice a winter, I need to clear it up a bit. Between snow storms the heat of the dryer air melts the snow already in the well, so it doesn't build up.