They should get along well together, from an aggression viewpoint. However, the Regal Tang is a large growing fish and needs a ton of swimming space for proper health. You would want at least a 125 gallon aquarium, and probably a 180 gallon or larger tank to keep this fish.
Also, you can not "upgrade" to a larger tank later, because the Tang family grows to 75% of its adult size within the first year of its life. By the time you upgrade, the damage is already done to its development.
For the reader... the Regal Tang is more commonly sold as a Hippo Tang, and more commonly known as Dori from the Nemo movie.