I'm British so have never heard of a "DEI hire". They make it sound like it's about hiring people that are not qualified, so I can only assume it stands for Don Jr, Eric, and Ivanka.
@selzero Just in case anyone looking at this wants the serious answer and can't be arsed to search for it: it stands for "diversity, equity, and inclusion". In saying someone is a "DEI hire", the speaker is implying the referenced individual got the job only because of their status as a minority, giving them priority over whites so that the company can point to them and say "see, we don't just hire whites". In other words, it's racist as shit.