First of all I don't know if there is any thread related to this subject, if there is my honest apologizes since I didn't see any where this was discussed.
So it seems all the nobodies known so far have exactly the same appearance that their somebodies form have.
Although this doesn't apply to Roxas and Naminé.
About Roxas it has been explain why he doesn't look like Sora since
What about Naminé?! Is there any special reason why she is so different from Kairi?! Or do you think Kairi harbors somebodie's heart within her but it has not been revealed yet?! The reason why Naminé has abilities that Kairi don't make me wonder about this as well.
So it seems all the nobodies known so far have exactly the same appearance that their somebodies form have.
Although this doesn't apply to Roxas and Naminé.
About Roxas it has been explain why he doesn't look like Sora since
Spoiler ShowVen's Heart is sleeping within Sora thus Roxas looking like Ven instead of Sora.
What about Naminé?! Is there any special reason why she is so different from Kairi?! Or do you think Kairi harbors somebodie's heart within her but it has not been revealed yet?! The reason why Naminé has abilities that Kairi don't make me wonder about this as well.