This is a common question we encounter.
Wall oven venting is usually accomplished via the front of the oven. The general idea is that all cooking is done with the oven doors closed and the fumes and smoke are contained within the oven. However, owning a wall oven myself, I can tell you that this is not always the case. Especially, if the food burns or is being slow cooked. With that said, we have installed hundreds of kitchens with wall ovens in them and we have yet to have a complaint about venting.
We did have one customer that was concerned about it so we installed a home venting unit. These types of units have a central blower, a single external exhaust, and multiple inputs. One of those inputs we placed over the wall oven.
It is a nice solution but does require extra installation time and cost.