If Biden isn't, but Hunter is, he presumably has been able to tell that the resident is not his father. In which case he would have some blackmail material if the WHs still want to keep up the pretense for whatever reason.

Also, other alternative I can think of, somewhat possible that Hunter has years ago made some deal with the WHs and has been giving them necessary information (the way that laptop was "forgotten" looks pretty suspicious), in which case the pardon might be what he gets in return, except maybe the WHs wanted that done in a way that makes the pretend Biden, and consequently, the people who got him into the White House, look as bad as possible.