I'm not sure that I have tried any IEMs marketed specifically for gaming but I do see them from time to time and I do use IEMs for gaming quite often.

I do have quite a few IEMs but one that comes to mind most vividly during my gaming sessions would be my Final Audio A4000. The sound is crystal clear and It is excellent at picking up distant ambient details. Placement and strength/volume of various sound seems to be just right. There is just enough bass to give some weight without being a distraction in other areas. While not being my favorite IEM for music it does feel like it was made for the kinds of games I like to play such as Star Citizen.