[Gatts]

Well - developers have decided and here is the exact list of "archers" that benefit from the scope bonus (and also scope + ale bonus):
Skeleton-Archer, Archer, Gunner[canoneer], Goblin with the Catapult [catapult goblin], Elf, Pathfinder[Hunter], Goblin [shooter].
(Only for a subject the Optical sight and the complete set of Archer’s Commander)


Here is list of all archers in da game:
Archer, Elf, Pathfinder, Gunner, Goblin, Goblin with the Catapult, Skeleton-Archer, Thorn-hunter, Royal Thorn, Evileye, Beasteye, Cyclops

(it is copy/paste from free fan manual - but all should know the original units by now)