In my opinion, there is a difference between the words of a lay man and a sangha in robes.
Yes there are bad apples within the sangha community, but on a whole if a monk can gain no benefit from lying, or if damage is possibly incurred from speaking the truth - I'd be inclined to believe what he says.
For example, as posted by WisdomBeing, what reason would this monk have to lie?
Advice from Dorje Shugden that His Holiness should leave and that He guarantees H.H. safety
From this article, "THE TRUTH behind who saved the Dalai Lama's life" it seems that HHDL and his entourage "depended" on both the physical man power of the Chushi Gangdruk and the power of puja/protector.
Besides the Chushi Gangdruk, HHDL brought along with them a thangka of Dorje Shugden. It was borrowed from his guru Trijang Rinpoche, which assured that HHDL has a safe escape from Tibet. Upon arriving the thangka was returned to Trijang Rinpoche. Attached is the actual thangka that the Dalai Lama carried in a container on his back throughout the whole 1959 exodus.
I like what vajratruth says, "Even an ordinary person will never forget important people in their lives. So how can Chenrezig forget and turn against the Protector sworn to protect Tsongkhapa's teachings and who saved the human life of Chenrezig's emanation."
Accounts like those of the Chushi Gangdruk really makes us think about the possibility of the "bigger picture". How can Chenrezig forget the kindness of Dorje Shugden. Impossible.