Hm... you have a point there. However, either my memory fails me, or there weren't any FM scenes with Lexaeus, Marluxia, or Larxene in them... so what about their absent silhouettes' battle quotes? Would be odd to have the others with English lines, yet have them remain in Japanese.
Why would they need to have them record anything new? Their battle quotes and grunts are already saved from Re:CoM...They can just stick those in. If they did want to go with a clean slate and start brand new, all they have to do is call them in and pay them for their work. It's not a complicated process.
Edit: Ninja'd by Sign