I think it would be morally reprehensible to solicit someone who you turned down. To accept a donation on the other hand, I personally see no issues with it. The donor is offering the money (perhaps naively thinking it will get them another shot at acceptance – as long as the school doesnt lead them along this path then) I see nothing wrong with accepting it.
A number of years ago when our first child was entering elementary school, we dutifully filled out an application for a particular school and they simply ignored the application (yes, we called and confirmed it was received and was being reviewed) and obviously had no interest in us as parents in the school or our child as their student. That’s fine, and in our opinion, their loss. However, when they called several months later following up on the invitation they sent to their annual dinner, we politely asked them to remove us from their mailing list. They did.