I know white ulcerous growths can be LLHE which a main treatment is Vitamin C.
I do not know about fresh water baths since I have never done them.
I would email
techsupport@drsfostersmith.com with your description and preferably some pictures which show these "spots". They have marine biologists and I think they are a good resource in addition to reef central. I purchased my Regal from them in August of 2008 and it did not have any disease issues. I would get a jump of treating this fish since it looks like it is in the early stages of whatever is bothering it since it looks pretty good to me from your pictures?