Hypo is one method. Another one is to treat the QT tank with Copper to help with Ich if you want. Also soak seaweed and other food in Garlic Guard to help their immune system.
IMO there is nothing you can really do to prevent Hippo tangs from getting ich. I know people always say if you QT for 6+ weeks and don't notice any ich you will be ok and you won't introduce ich to your display tank. Personally, I have never seen that really work as planned. It sounds good in theory, but Hippo Tangs and Powder Blue Tangs seem to get ich randomly. At the LFS I work at we put a Powder Blue tang in QT for 8 weeks in copper, then put him in the 400G Display tank, within 2 days it had ich spots on it with no other fish in the tank that was setup for 3 months cycling with 800lbs of live rock. To this day (over a year later) I see Ich on it about once a week, only 3-4 spots at a time, and usually shows late in the day before lights out, but it is definately there. Doesn't seem to hurt the fish at all though (doesn't scratch or act erratically) and the next morning the spots are gone. We have just learned to live with it and accept it is just "one of those things" with that fish. Now there are 4 tangs in the 400G along with about 5 other fish and no other fish has ever shown any signs of ich other than the Powder Blue.