If Biden was really racist, he would not have accepted to be Barack Obama's running mate in 2008.
That doesn't say anything about whether or not he is racist, it just says that he didn't turn down a golden opportunity. There are plenty of racist people who don't allow their bias to interfere with their career.
White people generally think racism is a white and black issue (no pun intended). There is TONS of grey area and nuance. Biden can absolutely support racist policies in the name of bipartisanship and accept Obama’s offer.
Is that closeted racism, to be blunt?