I am confident about this. I have read more than a hundred books on Tibetan Buddhism. I have attended teachings and retreats with dozens of teachers from many lineages. I have been an Aro apprentice since 1997. If something in Aro were wrong, I expect I would have found it by now.
The doctrines of Aro are all mainstream. As far as I know, Aro does not have any type of practice that is not found elsewhere. (I discuss this in more detail on a later page.)
What is unusual about Aro is mainly not what it includes, but what it does not. Typically, Buddhist Tantra is presented as a system of ritual performance. Usually, the main ritual activity is chanting texts. In the Aro gTér, there is much less of this. Instead, it emphasizes silent meditation and non-ritual physical practices.
To the extent that what Aro includes is unusual, it is only in presenting the other yanas from the point of view of Dzogchen. This is orthodox in the Nyingma, but it is not common for it to be done so consistently. In fact, the more common presentation is the other way around. Dzogchen is more often presented from point of view of Mahayoga—that is, as a system of rituals and liturgy.
In fact, there are only two aspects of the Aro teachings that anyone has ever questioned. Those are the teachings on the nine bardos and on vajra romance. You can follow the links to find answers to those questions.