The Warlock's Eldritch Blast does half damage to objects. But Vitriolic Blast changes the damage type to acid. Acid does full damage to objects. So does a Vitriolic Blast do half damage or full damage to objects?
I'd say full damage. As far as I can tell, the only reason the "half damage to objects" clause in there at all is because a Warlock's Eldritch Blast isn't of a specific energy type, and therefore there aren't any other rules stopping it from causing full damage to objects. If it deals energy damage, however, I'd say it deals damage as that energy type normally deals damage.