In episode 349, Danzo visits Orochimaru.
One of the guards that Danzo takes with him, who is waiting outside, is Yamato, under the codename Kinoe.
Oro's testsubject that survived the injection of Hashirama's DNA was like 10 meters and a door away from Oro and
Oro didnt know.
Like 16 years or more later, Oro see's Yamato for the first time, when Yamato with Naruto, Sakura and Sai, appear at that bridge disguised as Sasori, to meet with Kabuto.
Edit: Episode 349 - Mirror 2.
Yamato as Kinoe appears at ~12:35 (its the little kid among 3 guards.
Yamato being one of them).
Yamato in episode 349 as a kid, is recognizable if you have seen him in episode 350.