I think background in landscape architecture is the concept of background....not +/- space. As mostly an artistic concept, I think you have to see both, so I am not sure blind areas on the hole strictly qualify either.
I learned about it in landscape design classes (actually pretty much in the first design theory class) but don't consciously recall using it. If I did use it subconsciously, I think it would have been in terms of shadows and light. Certainly, a dense, dark backdrop of trees and vegetation behind a green is negative space, offsetting the positive space that is the designed green.
Shadows can line the side of holes as well. And, I recall other cases where I elevated a green a bit, to make sure it stood out in the sunlight where the shadows covered most of the surroundings. I have seen fw stick out as sunny with shadows on the outskirts, although, typically only at the start and end of the day, rarely at noon. Certain shadows on steep sloped grass bunkers probably qualify as negative space as well.