With the exception of the K Series and Commercial Audio Series amplifiers, the answer is no*. The airflow technology that we use in our amplifiers is designed such that it is best to stack multiple amplifiers on top of each other, with no space between. The amplifiers draw fresh air into the front of the amplifier and exhaust it either out the sides and into the rack, or out the back depending upon the model. We want the hot air that is in the rack to vent out the sides or back, not the front. If any of these amplifiers are spaced apart with vented panels some of the preheated air will recycle to the front of the rack. The result is attempting to use preheated air to cool the amplifiers within the rack. The result will be loss of thermal headroom. If you choose to place the amplifiers with space between them, then use solid panels between them, not vented panels.
*K Series (discontinued) and Commercial Audio Series amplifiers are convection cooled so some space between amplifiers in a rack is recommended. Refer to the corresponding manual for these, and all Crown amplifier models, for specific recommendations.