I'm not sure the DOJ can legally comment to these senators on the ongoing investigation unless they have a valid reason that impacts laws being implemented. The conflict of interest question seems kind of weak.
Besides, who in the DOJ is going to give Hunter an edge in this? Everyone knows he's guilty on tax fraud so if anyone stick their neck out for him, it'll be like the Secret Service coverup deleting texts. Look how that's going for them.
Hunter will be found guilty no matter who's in office.