A recent modification to the git repository required changes to how the jME3-bullet-natives.jar file is structured (instead of libbulletjme64.so, it wants x86_64/libbulletjme.so, for example). I’ve made these changes and uploaded them to my git branch of jMonkeyEngine:
I didn’t see jME3-bullet-natives.jar within the original jMonkeyEngine master and it doesn’t look like it is being built (unless I’m just missing it somewhere?), so I’ve been using this JAR we put together awhile ago. It does include bullet 2.82, which appears to be the latest.