That’s true. The high poly models are close to the actual volume. It’s still a little inaccurate when the model has curved surfaces, but it’s definitely possible to design a monolithic dome or something curvy in SketchUp.
Edit: This is most accurate volume I could get on a house-sized hemispherical dome. I tried to make a higher poly one, but I decided to force quit after watching the spinning beach ball of doom for a few minutes. Had I waited, it probably would have given a more accurate measurement (possibly only a few cubic inches off). Either way, 2.98 cubic feet off isn’t that bad for a house that size. You’re right. It probably wouldn’t be a problem. Worst case scenario, someone uses a low poly curved surface to figure out the volume causing their estimate to be way off.