Definiately not the case for league tournaments. In the spring split of EU LCS they wore 3M Peltor ear defenders over small in-ear buds for their actual sound.
More recent tournaments they seem to have integrated ear defenders with headphones with Mic's on. (Previously they had 3 headsets, the ear buds for sound, the defenders then their sponsors headsets around their necks for the mic.)
More recent tournaments they seem to have integrated ear defenders with headphones with Mic's on. (Previously they had 3 headsets, the ear buds for sound, the defenders then their sponsors headsets around their necks for the mic.)