No new voices they just used current voice clips.
Actually, Scout has like 4 or something voice clips i don't recall ever hearing in any other voice clips currently in game like "Whoa, whoa" when his ears grow, "Hey, HEY,
HEY!" when Sniper steals the book from him, not sure about that "Ah!" when he freezes for a second before doing the thriller dance, i think i may have heard that one from the previous Scream Fortress, i don't think i've heard that "Holy crap!" when the second door rises up from the ground and his "Oh my God, oh my God, oh my God, oh my God!" when the skeletons appear
Then there's the MEDIC! song with certain instruments removed when the classes fight for the book and the Merasmus model with a mouth and actual facial flexes other than eye movement, and i guess the Scout's size changing ears can also count
But it is always possible that a person would go through all the trouble of doing all that themselves, still unsure about the Scout's voice clips though, so we'll just have to wait and see