I'm pretty sure that "recruit", in this context, means "expose to Y Combinator and encourage to apply if they have a good idea", not "give them a higher chance of being accepted because they are black".

Yes, they should and they are now. I think that Y Combinator understands that by not taking these steps, they are possible excluding people who may be the best candidate for the job. Y Combinator is simply extending it's reach with the intention of including more diverse groups of people, not giving preferential treatment to those groups. They are simply opening up a bigger umbrella.

. . . More diversity within YCombinator means more diversity of thought. If you have everybody who is physically and culturally similar within a company, or in this case accelerator, then creativity suffers. Also, it's a step in improving this racial gap within the tech industry.