When Ariakas talks about dominance and submission, he refers to a context in which the submissive person can choose to end the scenario at any point by saying a 'safe word', which essentially calls a time out to discuss what's wrong. If the submissive does not have the power to set boundaries in this fashion, or some other, then it is not consensual and I would not call it polyamory on that basis.
Lack of safe words does not equal non-consensual. Consent does not require safe words.
You can consent to enter a D/s relationship with no safe words, and in so doing, you consent to anything that happens within the relationship. You are still a legally free citizen with the right to end the relationship at any time you see fit, even the middle of a scene. Staying in the relationship constitutes continued consent to the things that happen in that relationship.
This type of relationship is sometimes referred to as "Master/slave" as opposed to "Dominant/submissive" in order to emphasize the level of control. However there are some Master/slave relationships which also use safe words, so you can never take anything for granted.
I have a friend who has a slave, and when they were setting up their relationship, it was the
slave who insisted that he not be permitted a safe word. He felt that for him personally, having a safe word would prohibit the feeling of total submission. It was a personal decision and he's never claimed that no submissives should have safe words, only that it was not appropriate to have one himself.
That being said, there were times where he's said "no" when ordered to do something during a scene. he would be punished for saying "no." You cannot, by definition, be punished for using your safe word.
But afterwards, they would discuss why he had refused the order. She knew that being a Mistress did not grant her omniscience, that there would be times when her slave would see dangers that she could not see. She likened it to a seeing eye dog preventing its Master from entering a busy intersection. She trusted his loyalty and knew that his refusal was an issue of safety, not insolence.
They've been happily married for 27 years, so I think it's safe to say, that's what works for them. She has other submissives with whom she insists on safe words. So there you have it: polyamorous with a relationship that has no safe words. Proof by example!