The antenna is designed for 435 MHz (68.9 cm) and the dimensions of corrugated horn antenna is 1.509mX2.16mX2.16m and its surface is not uniform. For such a lengthy horn antenna, does surface roughness has an impact on the EM signal.
It depends how the roughness compares to the wavelength and to the skin depth of the radiation in the material. Roughness that is large compared to the skin depth but with short repeat length compared to the wavelength in the horn will probably increase losses, but these kind of conducting losses become less significant as the horn opens out. Periodic roughness can create reinforced reflections and cause high vswr. A bit of buckling which is a few percent of a wavelength spread out over several wavelengths probably won't affect the primary beam. If you want low or controlled sidelobes and good cross-polarizarion then that's another matter. You need to state your wavelength and the size and length of the roughness to get more helpful answers. The effect at 30 GHz (1 cm)would be very different to at 300 MHz (1 m).
Unless you have some very extreme roughness, you should be fine. We studied this for 3D printed antennas and could barely measure the effect of the roughness.