I have a question about salt baths too. It seems a little complicated to keep the water at the right salinity. What's the proper way this is done when doing a water change? From what I've learned, you do a 100% water change every day when treating for Ick. For that, you have to keep the fish in a cup and re-acclimate him to the new water. The thing is, after a water change, he'll already be in salt water and adding more salt water to acclimate him could push the salinity too high or if you poured him back into the tank with the new water, it would still add extra salt from the cup he was in. How do you keep it properly measured?
The only way I can see doing it is to scoop him from the cup with a net and place him in the fresh salt water with the potential risk of shocking him with the fresh water (well, probably a minimal risk actually if you got your mix right)
To answer part of your question, I know it works for ick as I learned a few weeks ago.