Let them call Hunter Biden
Like it or not, if Joe is the nominee, we are going to hear the word "Hunter" more than we heard "email server" in 2016. Trump's entire game plan is to convince a razor thin margin of cynical centrists that "both sides do it" when it comes to using political office for corrupt personal and family enrichment. Not calling thr GOP bluff on Hunter furthers that narrative by making it look like we think the Bidens have something to hide.
Let them call Hunter. Every Dem senator can then ask him rhetorically over and over if he has any knowledge whatsoever of the crimes being tried, and when he says no, they can use it as an opportunity to put the senate GOP's behavior on trial.
In the end, Trump is going to be acquitted. The whole point of this exercise is to put the complete set of facts in the record and force the GOP to excuse blatant crimes in front of the electorate and the eyes of history. If getting that complete set of facts means Hunter Biden has to spend a few hours rolling his eyes at GOP clown antics, so be it.