Based on what I've seen, (We have footage of Swn playing as a Drow in some of the gameplay previews without seeming to suffer any ill effects, then again Early Acess and therefore subject to change) and based on how the day/night cycle works (i.e. none, party and quest during the day, rest at night) and based on the assumption that the tadpole should confer the same benefits to our companion/player character Astarion the Vampire Spawn, we shouldn't be expecting Sunlight Sensitivity to affect our Underdark natives. We probably get more unique dialogue options when discussing our origin, or people reacting as appropriately when seeing an Underdark native go topside.
