I am a vet, and I have seen my own dog start shivering with cold while hunting in thick cover that was wet. She was an English setter. I was very cold too, but temps were only in the low forties, but with a drizzling rain and heavy cover we were both soaked. Hypothermia can set in on any body in those conditions. My point is to watch out for your dogs as well as yourself. I would think at temps well below freezing the wetting of the coat is not a problem. Being dry at those low temps is easier than being wet at higher temps, for the dog that is. I was in NE one time and met a fellow Georgian staying at the same motel. He had three dogs staying under a "dog house" of sorts, sleeping on the truck bed, bare metal! The structure had a six inch gap all around the bottom for ventilation!!!! and a tin roof. It was homemade from 2x4's and house siding boards. No straw! I told him if he didn't go get at least some wheat straw for bedding I would call the local Vet and the police. It was criminal what he was doing, hunting those dogs hard and making them sleep on the metal in below freezing temps! Please do not think I am implying that anyone on here is doing something like that, because I am only saying though, that there are some awfully ignorant folks out there, and that guy was one of them.
If your dogs are dry they will enjoy it, IMO which is what everyone else is saying, but if it is raining and the cover is wet be careful. Another of the dangers is in mild weather turning off cold and partially freezing ponds where the dogs can break through, and they can't get out. That's a sad way to lose a dog! Take water for them to drink too even when it is so cold they need to drink. Have fun and enjoy your hunt!