My knowledge about the 17th Karmapa came from the book: The Dance of 17 Lives: The Incredible True Story of Tibet's 17th Karmapa. According to this book, the 16th Karmapa had several heart sons, Sharmapa being one of them. After the death of the 16th Karmapa from stomach cancer, the search of his incarnation revealed two candidates:
- Ogyen Trinley Dorje recognized by Situ Rinpoche and Gyaltsab Rinpoche
- Trinley Thaye Dorje recognized by Shamar Rinpoche
All Situ Rinpoche, Gyaltsab Rinpoche, and Shamar Rinpoche came from Kagyu lineage and were very close students of the 16th Karmapa. All three of them came to the 14th Dalai Lama asking for confirmation of the incarnations. Dalai Lama, through his divination, confirmed that Ogyen Trinley Dorje is the 17th Karmapa.
What I want to clarify here is HHDL was not interfering in the process. He was only asked for his confirmation.
As for additional information, Ogyen Trinley Dorje was also recognized by the Chinese government as the 17th Karmapa. Ogyen Trinley decided to join Dalai Lama and Tibetan Government in exile after refusing to comply with the Chinese government request to condemn HHDL.
Personally, for a lay practitioner like me, I have no idea which Karmapa is the right Karmapa. But I think, an incarnation should be judged by what s/he does in this life to benefit others and not by the virtue of his recognition.
Having said this, drawing an analogy from the whole situation to the DS situation, I think in considering whether the ban on DS is justifiable or not, would very much depends on whether the practice of DS really benefits beings. As we can see from the testimonial sections in dorjeshugden.com, many people have benefited from the practice of DS.