dented oil pans can wreak havoc on your oiling system. theres a tiny gap between the pickup and pan and if that gap gets even smaller, you can risk cutting off the oil supply to your engine drastically. id go for the pan first.
if hes only replacing the lower oil pan though, he wont be taking off the upper pan.
have you thought about the dent being the reason the chain is rattling?
chains arent supposed to be replaced under normal circumstances, theyre supposed to last the life of the engine.
also think thant if you replace the chain and guides youll have to remove the oil pan anyways. yor can just kill two birds with on stone buy replacing the chain and guide if your gonna change them anyways