Hi Rory,
I agree with Sara, I think avoiding trigger situations where the behavior is practiced is helpful and necessary in a stressful environment like the shelter. If the dog has a propensity to display the behavior, stress can exacerbate the likelihood or severity of the response (or even where it shows up).
I do like working dogs on training plans while they're at the shelter (it's enriching, helps us learn more about the behavior, puts the dog on our radar for support, and hopefully sets them up to have other ideas about guarding in the future). When I was at Animal Humane, we used a shortened "Mine" protocol that we had a fair amount of success with - with dogs that were food guarders. If the dogs were guarding other stuff, including toys, high value chews, we didn't have nearly as much success. That doesn't mean that the dog shouldn't go up for adoption with disclosures (another conversation about counseling and adopters in your community), but I think having an idea of how sticky the behavior is, the severity, the contexts that it appears is all helpful for placement. IMO, that information doesn't come from one assessment; that's where working with the dog really benefits your counseling.
And yes, while not all dogs that demonstrate resource guarding in the shelter are reported by the adopter to show the behavior in the home, it is more likely to occur if it pops up in the shelter. And as Seana mentioned, we have no idea about how severity is related to the likelihood of occurrence in the home. This is a very important piece of the puzzle, IMO.
As for research about the effects of free-feeding, this paper - Lyle, J., Kapla, S., da Silva, S. P., & Maxwell, M. E. (2017). Persistence of food guarding across conditions of free and scheduled feeding in shelter dogs. Applied Animal Behaviour Science, 191, 49-58 - suggests otherwise and reports while dogs in free-feeding and scheduled feeding conditions decreased in their food-related aggression over time, there were no differences between groups when compared. I haven't dug deep into it, but I've attached it here.
Good luck - and please let us know how this works out!
Lisa
#AnimalBehavior,TrainingandEnrichment