The Bullet 3.x B3_PROFILE can be customized using b3SetCustomEnterProfileZoneFunc/b3SetCustomLeaveProfileZoneFunc defined in Bullet3Common/b3Logging,
so you can hook Bullet 3.x up to your profiler of choice.
The Demos3/BasicGpuDemo will show the Bullet 3.x timings inside the Bullet 2.x btQuickprof profiler.