The essence of his training triggered the most ancient form of the White Lineage, which comes from the time where all Tantras originate. It goes back to a time where there was not much difference between nowadays Hindu Tantra and Buddhist Tantra. It is a profound path of truth, the path of the Vidyadharas, the immortal wisdom holders, and the path of the Rishis, the seers and speakers of truth only. Thus, Tulku Khyungdor Rinpoche is a representative of the White Tradition.
I'd say this is worthy of raising eyebrows.. Just because it's too convenient
of a setup to a whole mishmash of different views, techniques,
and even made-up practices that stray far from authentic lineage.
But I'd certainly be interested to see if the letters
claimed from Mindrolling Rinpoche and Penor Rinpoche are authentic ,
I'm guessing representatives of theirs could tell us this.
If the letters are valid then I'd still keep an open mind, albeit
very cautious. Also, on the Akasha yoga site he
says Khyentse Yangsi recognizes him, so that should
be easy to check.
This Yoga system is part of the heritage of Tulku Khyungdor Rinpoche, who according to Yangsi Khyentse Rinpoche, is the last holder of the lineage of Dorje Lingpa (which is the lineage of Vairocana).