yellow tangs are usually really tuff, if the water is right. its the "head & lateral line erosion" that they as well as other tangs get more often. in my experience all butterflies are more prone to ich. yellow tangs are the bomb though.
Do tangs have a tougher time with medications. I just treated my tank for ick, my angels and clowns are fine, but I lost my hippo and my yellow and sailfin aren't looking good/