I don't see how racism could the thing that kept Jimmer out of the league - especially after he'd bounced around the league for a few years and was dirt-cheap to sign.
IMO, it's much more likely that the NBA didn't have many places for a short, ball-dominant scoring guard that was a defensive liability.
It's also clear that Jimmer - for whatever reason - was never really able to get comfortable and make the most of the NBA opportunities that he did have. I remember the Phoenix game at Utah in 2019 - when Jimmer checked in, he got a standing ovation and then proceeded to go 1-10 shooting in garbage time (including 0-5 from 3). His +/- that night was -25 and he looked painfully bad... so bad that crowd went wild when he finally got a layup. Look at Jimmer's career stats - he has a ridiculous FG % everywhere he goes except the NBA. IMO you can't blame racism for that.
It's just the nature of the beast, but the line between success and failure in the NBA is razor thin and players have to capitalize on every opportunity they get. That's what got Jeremey Lin his big break; that's what turned Wesley Matthews into an NBA starter after initially signing a 10-day contract with the Jazz.
Jimmer had plenty of teams and plenty of chances to stick. I'm as disappointed as the next guy that the NBA didn't pan out, but ultimately it's no one's fault but his own. And frankly, it might ultimately be better for him to be the biggest fish in a smaller pond.