Thomas was appointed in 1991. I don't think DEI was even a thing then, so no I don't think he was a DEI hire. Race may or may not have had something to do with the hire, I don't know. I do think Ketanji Brown was a DEI hire though. Biden made it known that his goal was to increase diversity with his hires/appointments.
Vivek is part of the trump campaign and there is no way he is there to meet a DEI quota, he is there because he is damn good at what he does. There are a lot of black people who are not dei hires, there are a lot of black people who are dei hires and still were the best candidate for the job, and there are a lot of black people who were dei hires and were under qualified and also under performed. (this can be applied to any dei minority)
The fallacy about DEI is that not all people who are DEI hires are going to be good or bad hires. Some will be qualified, some will not. The downside of DEI hiring is that sometimes it is assumed that all minority hires are due to DEI and therefore people may assume they are unqualified.
DEI becomes a problem when you try to force a certain number of people into a specific position just to meet a quota. If you try to get more minorities into a position than there are qualified applicants, then you are forced to accept unqualified applicants just to meet the quota. This is not helpful for anyone involved.