If at all, then it would be extremely rare. The reason is that to generate the large transmit power levels required of radars, the high-power amplifier is typically driven into compression, meaning it is not functioning as a linear amplifier. This means that the output pulse envelope is distorted towards a rectangular pulse anyway. Generally, pulses are used with rectangular envelopes. However, while the pulse envelope may be rectangular, that is not to say that the Energy Spectral Density (ESD) of the pulse needs to be rectangular or otherwise excessively limited, since phase modulation of the rectangular pulse can create a wide variety of ESDs. This is the reason for Non-Linear FM chirp waveforms, for which a Gaussian ESD can indeed be generated.