One problem with as eccentric on a motor is that you have no control of amplitude. You can't vary the amplitude by changing speeds. In fact, the force goes up as the square of the speed, so at higher frequencies, the vibration level is much, much greater.
I'm certain you can break boards this way, but trying to quantify the results would be tough.
Ir'm not familiar with the standards off the top of my head, but the requirements may call for constant displacement, constant velocity or constant acceleration over the range of interest. To approximate these tests, you need to be able to control the frequency and amplitude of vibration. Since resonances can be high Q, you need pretty tight control of frequency. If you have jumps in the excitation frequency, you may miss resonances entirely.