Most fish in captivity are sort of forced into being omnivores. Most captive tangs will not pass up any type of food introduced into the tank, unless they are sick or stressed. The important part is offering a balanced diet for all of your fish. Feed a variety of meaty foods and plant matter. Just as important as the food is the dietary supplements to go with them. Soaking your food in products like Vita-Chem and Selcon will introduce [acronym="Highly Unsaturated Fatty Acid"]HUFA
[/acronym], ammino-acids, vitamins and minerals important for proper nutrition. In the case of your tang, it will eat pretty much whatever you put in the tank. As mentioned, they are grazers so make sure you provide it with seaweed daily.