I have a lot of experience with atlantic blues and I can tell you that they would not be a good choice for two reasons. First, I would definitely not try it unless you have an extremely large tank. Because both fish are blue (atlantics are only yellow as juveniles), the hippo will not accept him very well.
Besides for that, atlantic blues are one of the worst aquarium species as far as tangs go (only behind achilles and convicts) because they pick up infections quite easily when they are taken out of schools. If you are lucky enough to find a tank raised atlantic, I would jump on the offer, but otherwise, stay away. For no reason they usually start to lose their color and get bodily infections no matter how well you keep them fed or how much you put nutrients in their food. I have seen them come in to pet stores eating very aggressively and acting very boldly, and for no reason, begin to break out.