Ok, first of all, the oil pan is not aluminum... why would an oil pan rust if it were aluminum??
Second of all there is no gasket between the pan and the engine. it is a silicone sealant(RTV) use from the factory. You can drop the pan and bang that dent out, just be carefull and maybe use a peice of wood to cushion the blow a little. Then use High temp Silicone(rtv) to replace it. It definately looks like someone jacked up the car on the oil pan.
Tom