Vita-chem is okay to use all the time. It is a supplement, not a medication. Though it can be hard to find, I absolutely swear by it for healthy, robust fish. I also did a google search and found a forum where they discussed the use of vita-chem for hole in the head disease in betta fish just a few days ago, as before that I didn't even know that disease existed!
Honestly, like I said, I don't really know a lot about fish diseases. I don't know how to cure hole in the head disease and if aquarium salt would do anything at all. :(