I believe the answer to that will be maybe yes and maybe no.
Reason being is that there can be two possible light sources in flash photography, ambient light and flash. The flash duration is sufficiently short to be able to stop motion blur. But if the ambient light is strong enough and your shutter speed slow enough there could be a slight amount of blur noticeable in the image. The flash portion of the exposure will create sharp detail but the ambient portion could capture some motion blur that would give the appearance of softness. So if the shutter duration is short enough to eliminate the ambient light from the exposure with the flash being the sole source of illumination then shutter speed becomes irrelevant (as long as sync speed is maintained). But if the exposure includes ambient light then shutter speed will become important and to slow a speed may show motion blur.