For sure it is important to have confirmation from other high Lamas. Also, the incarnation status of tulkus are often and almost always confirmed by the protectors in trance, through oracles. So I believe this would probably also be sought as further confirmation, and would have to match the divinations / visions / dreams and confirmation of the high Lamas.
Beggar, your post got me thinking. Kyabje Drakpa Gyeltsen, if recognised and enthroned would be one of the most powerful forces in the Tibetan Buddhist world, and THE most powerful in the Shugden movement. The CTA would be trembling in their beds just considering this possibility. Therefore, should Kyabje Drakpa Gyeltsen ever decide to reveal himself, who would recognised him? Who would enthrone him?
Considering the high Shugden lamas alive today, the most likely to dare recognise Kyabje Drakpa Gyeltsen would perhaps be Kyabje Trijang Rinpoche or Gangchen Rinpoche or Pabongka Rinpoche. Yongyal Rinpoche or Gonsar Rinpoche are possibilities too. Unfortunately, most of the eminent Shugden lamas are too young at present - think Domo Geshe Rinpoche, Zemey Rinpoche or Rabten Rinpoche. Or they are in hiding (such as Lama Zopa, Gehlek Rinpoche or Khejok Rinpoche) and would not reveal themselves by doing such a thing. Or would they, knowing that such a recognition would change the tide of Tibetan Buddhism and allow them to be true to their Gurus once again?
Another thought - imagine if the Dalai Lama were to recognised Kyabje Drakpa Gyeltsen! The Dalai Lama obvious has the clairvoyance to know, even now, whether it were true that Kyabje Drakpa Gyeltsen was alive. The Dalai Lama would definitely be able to recognised him. I mean, he has recognised so many other reincarnations already. But what a slap in the face that would be, not to mentioned being detrimental to the Anti Shugden movement if the Dalai Lama himself were to announce that Kyabje Drakpa Gyeltsen has reincarnated. How can a demon or evil spirit reincarnate as a human? Much less as a high incarnation?
I'm sure since this announcement was made, the supporters of Kyabje Drakpa Gyeltsen, those who know that he is alive, would already be considering these facts. Perhaps they are even planning to request the oracle of Shugden or Setrab or other deities to recognise the new incarnation. Previous life recognising a future life? Surreal yet entirely possible.