Please correct me if I am wrong:

Think of it this way: I was under the impression that, the Bon were assimilated into the Tibetan Buddhist lineage traditions. They are a valid Shamanic - Buddhist lineage.

Many other faiths did this, take the Celts. They were assimilated into Christianity and chose Jesus and the Trinity as their meditational deity. They also imported many of their customs and practices and tailored them towards Christendom.

The Bon are Buddhists, and their yiddams/meditational deities are just as valid as the Buddhist ones. They were assimilated into Buddhism. If your mind cannot turn that way, there may be obstacles to the practice.

Master Wangyal is an excellent teacher. If he has accepted the validity of these Bon deities. It is Ok to assume that they will be beneficial.

Have a wonderful retreat!