Olive oil is never used in the dough. I have seen different kinds of oils drizzled on before and after baking. Not sure what is "official", but my personal preference depends on the quality of the toppings. If I have am using a really good fresh buffalo mozz and fresh tomatoes, I try not to add anything to get in the way of those simple but splendid flavors. Otherwise, I drizzle a small amount of quality extra virgin oil on at the end. You should try different approaches and see what you like, but if you're baking a real Neapolitan pie, don't put any oil in the dough.