Regarding (1), it only expands the labor pool if the pipeline for "diverse" labor hasn't already been exhausted. Instead we seem to see employers competing for "diverse" labor, including in some cases foregoing technical qualifications for "diverse" qualifications. This is only in the company's best interest to the extent that it's economically advantageous to appear to be striving for diversity.
Regarding (2), I really don't think most companies are to the point where they're deliberately stoking racial division as an anti-union tactic, at least not in the FAANG space. Seems like it would be a lot easier to push the political divide button which is pre-primed on account of the media.
Amazon tracks lack of racial diversity as a union formation risk metric https://www.informationliberation.com/?id=61403
“Management isn’t taking advantage of you; it’s the person sitting next to you with a different gender or skin color that’s the threat”
Corporate DEI stuff is also useful to "prove" that an employer isn't racist--current anti-discrimination law puts the burden of proof on employers to show that they didn't discriminate, and since it's not possible to prove a negative, they must instead compete to show that they're among the more 'woke' companies ("look at our DEI propaganda, how could we possibly be guilty of discrimination?").