Well, they seemed to bounce right back. After a night in the catch bucket in our laundry room, they were dry and feisty. I just gave them a deep with a couple frames of drawn comb and they took right to it.
I guess bees are more rain-resistant than I imagined. I just can't figure out why they wouldn't move under cover in the rain. If the cluster had moved just a foot farther, they would have been sheltered.