If you do research into the "7-day shut down," the rescue people involved "that breed that shall not be named" seem to say the shut-down should happen in a separate room, away from other dogs. Their breed has a reputation for dog reactivity, so I think that they may be onto something with reactive dogs -- being away from other dogs for a few days means the cortisol levels can come down from their elevated levels (from being in a strange place) without feeling vulnerable to other dogs. They know they're around but don't have to interact -- at least at first. It's stages of expectations.
With dog-friendly dogs, I've always done the shut down in an area where they can see and smell my dogs, but I don't let my dogs go up to the kennel. I want to control the introduction, later. I just want them absorbing the routine of our household, without the stress of having to wonder what to do or how to fit in. Some foster dogs are ready to participate in the household in just 3 days. Others take a couple of weeks.
The real challenge though are the dogs who don't know how to speak dog. They react because they're confused, and it's really hard to get them un-confused. My trainer does it over time using a stable pack in a large-field socialization exercise. I hope that's not what you're dealing with, but be alert to it.
I do really think the "shutdown" has enormous value for these kind of dogs. I came to it as a skeptic thinking it wouldn't make any difference, and I'm now 100% convinced that it makes a BIG difference in their transition. It probably won't solve dog reactivity though -- it just transitions them into your home and give you a chance to work with them with less fear and stress.
Anyway, food for thought.