I think it's likely. Namine was born in the exact same moment but appeared in Castle Oblivion where Ventus body is sleeping. She was also born with blonde hair.
I wouldn't say Ven had more of an affect on either though. Many of the things in Roxas life was due to Sora. Lack of memory, having a keyblade, being a nobody, his power, his dreams, etc. Nearly everything was an affect of Sora.
Only the face and second keyblade was due to Ven. And if you notice Sora, Ven, Roxas, Vanitas all have the same face model. The only differences are their hair and personality.
Where Roxas was born though could be tied to Ven or just random.