The more I look into these subjects, the more it seems to me that the ATRs are in many cases dealing with entities described elsewhere as djinn.
Mind, I am not implying that the whole of the Nganga, or what have you, can be reduced to a one-to-one correspondence with a djinn from another tradition. What I'm saying is that there appears to be a lot of overlap, and just maybe, in some cases, we are talking about the same "family" (genus) of spirits.
For instance, when dealing with what someone might call their "ancestor spirit," how would one practically distinguish between such an entity, and a djinn who is passed down the family line, a relationship born of an ancient pact or affinity?
Perhaps a greater understanding of both the ATRs, and the world of the djinn would be furthered by such comparisons.