Herb Ox:
First of all, there will most likely be symptoms of “Heat”, but not full Heat signs… more deficient Heat signs like "thirsty, but only want to sip; malar flush; heat/sweat on palms, soles, and chest; etc.)
Also, Yin Essence insufficiency can be one of the causes of Yin Deficiency, but not necessarily the only one, or the one that will always exist. In addition, the kidneys are likely going to be affected, regardless of whether they are the actual souce of the problem or not, because of its functional relationships with the other organs.
Di Gu Pi’s main strength is clearing severe deficient Heat syndromes that often manifest as very serious empty Heat symptoms such as “Steaming Bone Disorders”. And since Yin deficiency is typically involving either the lungs, liver, kidneys, or the heart (or all of them), then, yes, Di Gu Pi does have a positive affect on these organs. The action would be more to (1) clear deficiency heat, and (2) nourish Yin. And you are right… it does have a special action in clearing abscess in the Lungs due to Heat (especially deficiency Heat).
Action wise, “Cool Yin” would not be the case here, cause “Yin deficiency” implies that balance is tilted towards the Yang, which is why Heat signs persist. But because the Heat is due to a deficiency of Yin rather than an excess of Yang, you will see more deficient (also known as Empty) Heat signs versus excess (also known as Full) Heat signs. If you try to “cool Yin” down, you are only going to make the situation worse as you will cause the Yang to be even more excess. Unless you meant “cool Yin” by “making it better through nourishing and heat clearing”, which kinda implies what I meant in my previous paragraphy, then that would work.