If it isn't visible on bing, and we don't have a survey trace, then the question is always going to be how the information was derived.

This isn't so much about copyright, as breaching Google's terms of use. We don't want to end up with a tainted OSM. Survey the site, align the bing imagery.

Think of what you could legitimately place in the source tag. If you could place source=bing, or source=survey, then okay. If you would have to put source=google, then just forget it.

If potlatch can't handle it well, well isn't that an issue for potlatch?

As long as the landuse extends to the very edge of the road, with no gap in between the landuse and the road, then placing a gap isn't mapping what is on the ground.

Similarly when a park extends to the edge of the water..