It certainly is for proving privacy claims. Even finding vulnerability by reverse engineering is to debunk security claims, not to strengthening it.
You certainly can “prove” and “disprove” “security” by reverse engineering, to the same extent a source code review can (or even more, since you’re looking at what’s actually running on the device). It can often require a bigger time investment, but even that’s not always the case in my experience, especially if you’re working with a really bad code base.