Like you, I wasn't alive when Rupp coached.
My opinion, based on accounts I've read and heard, is that Rupp was not a racist but also cared little about integrating the SEC. I'm not saying he's a bad guy for that. I'm saying I think he was more interested in being a basketball coach than a social changer. If the SEC had black players in 1950, and he had a chance to sign some he thought would improve his team, I absolutely think he would have done it. But, I also don't think he would have cared if the SEC never integrated, so long as his teams kept winning.
If I wanted to pick at Rupp's legacy, I'd start with the investigation that led to his team's one-year death penalty, discuss that they were historically lucky that vacating titles apparently wasn't a go-to form of punishment then, and then wildly (and probably correctly) speculate that they were cheating for decades in ways that only Mr. Gilbert could top.