Mainly you can find references to the fact that many of the statues in India that were destroyed in the Tibetan Cultural Revolution of 1996 were blessed by Trijang Rinpoche, Ling Rinpoche and Zong Rinpoche.
Anyway, Ling Rinpoche was a great Tantric practitioner, and his Root Lama taught the practice widely, so there can be no doubt that he regarded DS as Enlightened. I imagine that he practiced quietly, as he seemed to do everything.
Generally, Dharmapalas are in the nature of secrecy. When many High lamas can to Manjushri Center in the 80's they NEVER even spoke his name, referring to him as "the protector" or just "Dharmapala." It is only as a result of the Dalai Lama's actions that this is a public issue at all.
As to who Ling Rinpoche's main protector was, it seems as though he felt that it was really his own business.