RE: Shooting Deer during rain (tracking)
I've taken a few in the rain.
I'd suggest doing as was mentioned above. Limit your shots to shorter range than you would shoot on a nice day.
One thing I've noticed, the blood trails seemed to have an excessive amount of blood. This was because the blood was mixed with the water on leaves and such making the blood trail appear to heavier.
I did not wait very long before tracking either. Because the shots were close I was able to make a very good hit and knew the deer were hit pretty hard and wouldn't go far.
Now I wasn't hunting in a down pour. It was more like a light rain.
I would recommend tracking very soon after the shot. Allowing too much time may wash the trail away completely.