Huey, Dewey, and Louie were already in Kingdom Hearts: Birth by Sleep.
Yes, and those three were well-known characters before
and after DuckTales. They were in quite a few Donald Duck cartoons, their own 90s cartoon series ("Quack Pack", was it?), and probably several "House of the Mouse" cartoon shorts in the 2000s.
By the same token, Chip and Dale have also appeared in the Kingdom Hearts games in minor roles, two characters that also had their starts in later Donald Duck cartoons. Note, though, that I don't think we've seen Goofy's "son" Max from Goof Troop, any of the Darkwing Duck cast, or any of the TailSpin cast. We didn't even get any of the Gummy Bears, despite having a ship
named after them in the first two Kingdom Hearts games on PS2.
On the upside, though, we did get Scrooge in Birth By Sleep, and although he existed in the comics for years before DuckTales I don't think he was ever in a cartoon before then. DuckTales is the cartoon he is best known for, though there's also Mickey's Christmas Carol. So I guess if Scrooge could appear in a minor role in Birth By Sleep, there's still hope.