They definitely don't fix the problem. As the sibling comment points out, diversity is a result of tons of factors - office locations, industry sector, compensation packages, pto, work life balance culture; and, most importantly, the diversity of the candidate supply itself (you're delusional if you expect a large deviation from graduation ratios).

It's sort of similar to hiring a "head of profit". Profit, like diversity, is the outcome of the entire company's operations.