Non iodized table salt will work, but aquarium salt is better. Keep them in there only for as long as you need to in order to get anti-biotics. It will dehydrate them--just not by too much
The bacteria screws up their ability to regulate water balance, and they start taking in/retaining water. It can kill very fast. Sort of like putting a saltwater fish in freshwater. The salt bath fixes the immediate problem and gives you time to get the necessary drugs.
If they dont have that, the salt bath will still fix the water balance issue. Thankfully most of the bacteria that cause that particular problem (there are a few, Aeromonas hydrophillus is another. Redleg will also present with bloating) respond to tetracycline. If you can get it, Baytril is more powerful, but in my experience vets not specialized with herps are nearly useless. I have had to teach myself how to diagnose and treat frog diseases through reading veterinary texts...