No there's no law that says you cannot pass a snow plow in Wisconsin or any other state.
So no it's not illegal to pass a snow plow in Wisconsin or any other state.
Still it's not a good idea and could cause a wreck as it's best to stay behind the snow plow as they plow the roadway for you to drive safely on.
If you pass the snowplow then you can end up in snow covered and ice covered roads where you could get stuck.
So I would not advise passing a snow plow as they are there to help you get to your destination safely by clearing the roads.
Stay behind them at a safe distance and let them do their job.
You shouldn't drive fast on snow covered or ice covered roads anyway so there's no reason to pass them unless you're an ambulance or police officer on the way to an emergency.
Also the law states that anyone following a snowplow in Wisconsin or any other state that you cannot follow a snowplow any closer than 200 feet upon any highway having the posted speed limit of more than 35 mph.