The description for Hexblade's Curse states the following:
You gain a bonus to damage rolls against the cursed target. The bonus equals your proficiency bonus.
Say that a Hexblade Warlock uses this ability, then commands a creature via any of the several Summon Aberration/Undead/Shadowspawn options available to them. If the summoned creature hits the target of the Hexblade's Curse, does its attack gain the bonuses to damage?
An alternate way of framing this question is "do the damage rolls for the summoned creature count as its summoner's own damage rolls?"