If you do have employees (or execs) bypassing the process or lowering their standards in order to meet short term goals, that in itself is a cultural problem the company would want to address.
Edit: it's worth noting that every manager who has more planned work than they can execute with their current head count already has a short-term incentive to lower their hiring bar and get someone in the door quickly. Managers get measured on executing to plan, so that's probably a stronger incentive than any bonus structure.
So my point isn't that lowering the bar to game the system will never happen, but that it's a failure mode that already occurs and that the system should already have defences against.
The point of this bonus is to encourage executives to recruit and hire from non-traditional sources, such as HBCUs.
And this is Microsoft we're talking about here. If they come across two very qualified candidates, they will hire them both. Not one over the other.