The pardon power is absolute and constitutional. Using it is never itself a crime. What's documented here is what happened immediately before each grant.
A donation followed by a pardon is a sequence, not a verdict. Some of these people may have had genuine grounds for clemency, and several maintain their innocence — which they're entitled to do.
Two things are documented rather than inferred: in one case the pardon application itself reportedly cited the donation, and in another the Campaign Legal Center filed a formal FEC complaint alleging a straw-donor scheme. And the official who used to vet these applications has said publicly that at least one grant "wasn't close" to Department guidelines. That's testimony from inside the process, not commentary from outside it.