There is no reason not to hook train a royal. You can, and if you feel more comfortable, you should. It is often not needed, at home I don't hook trained my royals.

At work however all the snakes and large lizards are hook trained or whistle trained depending on the case. It is a safety issue especially with a'rocks. Many of the brighter animals we keep (caiman and gators) have been trained further to turn and present tails for blood work and such as well. It is easier and far less stressful for both animal and keeper.