Drifting snow might be an issue if the snow was to completely cover the hood. But remember, the engine is under the hood mostly protected. To cover the sides where it was not protected, maybe a tarp or blanket to keep the snow out. We typically get about 4ft of snow accumulated over the winter where I live. But being in the forest, we dont really have wind. Though I have had snow drifts in some places, and they can get very deep. Parking your tractor where it will drift like that, maybe consider building a pole shed with sides?
Also, doing what bigtiller said works too. Thats how we always did it on the farm when I was a kid. The engine block heaters on all our equipment (semi-trucks, big articulating tractors, etc) were always plugged in. The snow would drift around them, and we never really gave it much thought as to covering the engines or anything. When ever we needed something, like to start the trucks to haul wheat all winter, they always started. Same with out tractors for snow removal. Just go out and start it, unplug it, brush the snow off, and get to work. When finished, park it and plug it back in.
But, to each is their own. You have to decide what will work bet for you and your situation. For me, my tractor sits outside next to my garage where it is easy enough to get to in deep snow.