Being from south Louisiana & spending a lot of time at camps, I have to say I have NEVER heard of putting olives in gravies. In fact, if someone at the camp put olives in the gravy, we'd probably figure he was drunk. I've had them in spegg sauce but never a "rice & gravy". This may be the new "tomatoes in gumbo war".
My favorite pizza is a pepperoni and green olive pizza. The saltiness of the green olives, which is an alternative to anchovies, combines well with the tomatoes in the pizza sauce and spices of the pepperoni. Unfortunately, I have to make them myself as pizzarias tend to have black olives only.