Maybe the ones in the red are unlockable characters and the only way to get them is to play through storymode.
All of the characters outlined in red are newcomers that never appeared in the previous titles, though the dinosaur wrestler from the Mexico team might be an alter ego of Tizoc. Most games in the series don't have many unlockable characters though, it's just limited to boss characters and other characters that are not part of any canon theme.
I also see Nakoruru in the first slot of the "Another World" team. :3
Not the choice I would've made if I was to take a character from Samurai Shodown, but she's the most popular character from that franchise... I would've preferred Shiki or Asura though. Loved them in NeoGeo Battle Coliseum!
I think Nakoruru is a solid choice. Besides the cute factor, she also has the "pet handler" gimmick working in her favor. They could of chosen Haohmaru, as he is the face of the SamSho series, but there already a lot of "shoto" characters in the game.