Also I think how someone lets their pack interact should be based on the pack and the person and what they are comfortable with. I myself am more familiar with behavior. I interrupt behavior that goes directly against my orders which is NO FIGHTING and NO AGGRESSION TOWARDS PUPPIES or young dogs.
I am personally comfortable with what you see in the video. If that were one of my males being challenged by a younger male then I would allow it to continue as LONG as it remained fair. Then again scenarios like this don't really happen in my house. If snarling ensues I help fix the issue. I would have told the foster to sit and behave to "back my dog up". If the dog in the "submissive" position is unstable and lacks recognition of the authoritative dog you must evaluate the reason. is the dog just dense? Is the dog actually challenging? Why is the dog challenging? is it lacking self preservation and going to result in a nasty fight? or is the dog slowly learning? Allow the dog to slowly learn in that case. The only reason I have seen fights break out in the scenario you see above is when a dog involved is unstable. That being said my dogs are personally very comfortable with one another and eating. They respect my authority and know that I will give everyone the same amount and there is nothing to guard or be upset about. So we don't see snarling. I do see snarling when a new dog enters the pack and is absolutely clueless about behavior. So I allow them to learn in a supervised and safe manner. The dogs are VERY fair and good at teaching so I sit back and let them do the work.
I don't create artificial structures or force someone to be submissive because I said so. But I do reinforce and back up what dogs say. If a submissive dog is being bullied, I will help them. If a dominant dog is being challenged by an idiot dog, I will help them. We are a pack. We work together. This varies depending on the pack
to each his own
"For the animal shall not be measured by man. In a world older and more complete than ours they move finished and complete, gifted with extensions of the senses we have lost or never attained, living by voices we shall never hear."