The database implementations tolerate concurrent access, either through inherent semantic guarantees of the filesystem, or respecting advisory locks. Some Crashpad client code maintained by our own team expects this behavior, so you can reasonably rely on it too.
The database implementations are stable in the “mostly unchanging” sense, and I wouldn’t expect version shear to affect safe concurrent access. If we were to make a change that might affect concurrent access, we’d be cognizant of the concern. I expect that in most cases, we’d provide a transition window.