Yep, you can call them in in the rain. Most of the time they will: not gobble as much, be less active, come in more silent, sit on the roost a little longer, seek and spend the day in openings. But if it is raining too hard, setting up on a bird that isn't gobbling much isn't a whole lot of enjoyable. And if you are going to hunt for consecutive days, getting your clothes soaked isn't always the greatest option. I'd go eat lunch and take a dry nap. (Hard to tell, but it is raining in the picture.)