Also according to this Garab Dorje is a Nirmanakaya emanation of Vajrasattva...http://www.amnyitrulchung.org/lineage/m ... rab-Dorje/
This is a site in the lineage of HH Jigme Phuntsok another great Dzogchen master of this past century. I have not listened to the replay yet so I will be interested in how ChNN explains Garab Dorje as a nirmanakaya manifestation of Shakyamuni!
I think when you get hung up on ascribing some sort of personhood to some Buddha someone is considered to be an emantion of, you have this problem. It's like creating some kind of geneology rather than observing that realized nirmanakayas are emanated from the sambhogakaya aspect of ultimate realization. We often call the latter "Vajrasattva." As such, the nirmanakaya Shakyamuni is equally an emanation of Vajrasattva as Garab Dorje. Or one could look at it like the ultimate realization of both Shakyamuni and Garab Dorje--and indeed any Buddha--is "Samantabhadra." When things like this are said, though, it throws people off because they understand that a specific Buddha named "Samantabhadra" realized Buddhahood like in this and that way. But they don't understand that we also use the explanation of an actual Buddha named Samantabhadra and how his liberation occurred as a metaphor for how beings can either realize buddhahood or fall into samsara based on knowledge or their lack thereof. One must know the context to understand if a so-called 'specific' Buddha is being spoken of or a didactic method is being used.
Also, this context of speaking of "the sambhogakaya level of ultimate realization" is where I feel grounding in Madhyamaka can be really, really helpful, since it will help people from making the mistaken leap of logic to interpreting "the sambhogakaya level of ultimate realization" as some sort of singular "thing," like a truly existent field like a shared consciousness or something, rather than being uncompounded and free of the extremes of "one" or "many."