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If you were hired by Yamaha or any music program company like Crypton or AH-Software to provide your voice for a Vocaloid, then yes, but not just anybody can provide their voice for a Vocaloid.

They have contests that, in the future, might determine voice providers. NicoNicoDouga is another way to gain thier attention by popularity. So, just know, if you want to be a voice provider, it will be a long road. You don't just ASK Crypton or Yahama or any Vocaloid company as most have a schedule their working to, for example, CFM currently have no plans to release new vocals while their updated and creating english versions of old. Zero-G create vocal specific vocaloids and Internet co rely on professional singers.

UTAU is a free alternative to Vocaloid and you can make your own UTAU with your voice for free.

Answer 2:

Just for letting you know, Zero-G Ltd. is holding a contest for an American Vocal. Just sing a song and send it to them.