Most often, heavy rain will hole them up until it's over. However, there are exceptions to this. Many years ago, I had been watching a group of bucks. One night after dark, as I was motoring back to camp during a torrential downpour, there they were-feeding out in the open desert country, just like they did in good weather conditions. I guess they were used to being rained on in the sparse cover desert country so it didn't bother them.
I love hunting during rainy weather. As many here have said, rain will keep your scent and noise down. Don't go back to camp! Bring your rain gear and prepare yourself for staying out in the weather.