Here's the real problem: Universities are expensive places to run and need huge resources to build buildings, hire and retain faculty, and other costly endeavors. Hence, the need for donors. Once you have donors, it is VERY hard to avoid this sort of tit-for-tat deal.

The best way to get around the funny business: have a system where students are classified into bins. Be very clear with donors: if a student isn't in the "top bin", they will not get in. However, in that bin, allow the "donor connection" to influence admission.

Is this perfect? No, of course not. But it accepts the reality of the world without perverting it too much. And honestly: can you really predict if one student is going to do better than another because of 1pt on some standardized test?