I don't think deer will bed down for an entire day if it's raining. Deer have to eat, something like every 4 to 6 hours. Think about it. Most of the time, during hunting season, it's rather cool to down right cold when it's raining. Even with all that fur, deer have to burn calories to keep the internal stove blazing.

I'm sure that they may bed down for the first few hours on a rainy day, but after that they're up and moving. Hunters see lees deer during rainy weather because most hunters head for home/camp. Those who stay in the woods may not see any deer because of all the noise. Think about it. Ever notice how when you're sitting in your stand/blind and it's really quiet, you seem to be able to make out every little detail your eyes see? Your brain has literally decided to not rely on your senses of smell and hearing, instead focusing most of it's power on your sense of sight. When it's raining, however, there's tons of noise, and your bain devotes much of its attention to that sense, instead of sight. Just rambling....sorry