I have never heard of a hive actually suffocating.
Even in the deepest of snow, the snow usually melts away, or allows at least a small amount of room for air to move.
Snow is a great insulator. As long as your hives are tilted forwards to allow the melt to run off the hive and not into it, they will do fine.
Most of my hive have a secondary upper hive entrance or at least a screened hole. (Not to be confused with a top entrance) But some do not. In either case, I do not worry about the snow.
Here are some nucs. Note the dead bees in the snow..
Of course, this is before the new 12 inches or more were getting today....