That's a very good question.
Who should be accountable for pointing out discrepancies? I would say hiring is the prerogative of a provost or a vice-president academic, in relation to a dean or a chair. It's not necessarily HR, per se, although HR may implement practices to close those gaps.
I like your question, because it highlights accountability. If you know there are gaps among assistant, associate and full professors across racial lines, whose responsibility is it to identify and ameliorate this proactively? I believe it's the chairs, deans and provosts who should do this.