CTR,
In none of the videos of the SB-1 have I seen the tail prop rotate even a few degrees. You may or may not know that in ground shake tests of helicopters/tilt rotors the gearboxes are routinely replaced with non-flight components prior to start of the tests to insure the bearings on flight hardware are not damaged. The vibration levels components are exposed to during these tests are, in most cases, less than or equal to those exhibited on the basic aircraft during operations.