The key, and something you would want to consider if you are building your own set up, is having even heat distribution or at a minimum, consistent heat in different zones of your cook surface large enough to work with.

A pure indirect heat grill probably doesn't get hot enough to do what you would want on a flat-top grill.

A direct heat source works if it is evenly spread under the grill surface or if the griddle is thick enough (and preheated long enough) to get the heat spread evenly across the griddle without overheating spots directly over your heat source.