It seems to depend on the region. Some use it and some don't.
Many also NEVER add olive oil in the dough. They just brush it on before adding the toppings.
Kimmie posted a recipe that includes semolina at
www.cheftalkcafe.com/cgi-local/ubbcgi/ultimatebb.cgi?ubb=get_topic&f=2&t=000251 
My own formula is:
1 tablespoon dry yeast
1 cup warm water
1/4 teaspoon sugar
1 teaspoon salt
2 3/4 cups all-purpose flour (unbleached)
It works very well in the KA with dough hook. I knead it for 8 - 10 minutes. 2 rising periods - first, about 1 hour, or until double in bulk, second about 45 minutes.
Divide in two and shape into balls. Cover and rise again for 15 minutes, while you work on your toppings.
I bake it at 550 degrees F in the bottom of the oven, on pizza stone, for 10 minutes.
[ May 22, 2001: Message edited by: pooh ]