IMO, I think it depends how you treat her. After Xion and Axel became friends, Axel began to see her face. Saix sees her with her hood, meaning he treats her like a doll and, he makes a small reference to her being a replica. There's also Xigbar with his "poppet".
I believe DS is a new character, though he might know TAV and their Master. Perhaps int he past he did something he was ashamed to do and decided to hide his face... or he's planning revenge like AtW hid himself as "DiZ".
Not only does BbS connect MX, Terra and Ventus to Xehanort, XH, Xemnas and Roxas but, in Days, there are some moments where Xemnas seems to treat Roxas like he knew him. Example: There's a scene where Xemnas taps Roxas' shoulder, there's another scene where Xemnas tells something along the lines of "So, you're sleeping once again."
Ventus looks like he's 14 - 17 years old. In KH1, Sora is about 13 - 14 years old. Since BbS takes place 10 years before KH1, Sora should be 3 - 4 years old, so if Ventus were to be his father, Sora would have been born when Ventus was: