The evidence is stacking up.
From
Of the Ruin of Beleriand and the Fall of Fingolfin:
Quote:
Sauron, greatest and most terrible of the servants of Morgoth, who in the Sindarin tongue was named Gorthaur, came against Orodreth, the warden of the tower upon Tol Sirion. Sauron was become now a sorcerer of dreadful power, master of shadows and of phantoms, foul in wisdom, cruel in strength, misshaping what he touched, twisting what he ruled, lord of werewolves; his dominion was torment.
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And:
Quote:
Then Sauron made it into a watchtower for Morgoth, a stronghold of evil, and a menace; and the fair isle of Tol Sirion became accursed, and it was called Tol-in-Gaurhoth, the Isle of Werewolves.
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I think we can consider it definitive that Sauron was certainly a little boy who liked playing with dogs in the First Age. The interesting question then becomes: why not later as well? One possible answer is that after he let much of his power pass into the Ring he was unable to. There are probably others.