Your message title says Google Voice, but the body of your message appears to be referring to Voice Search. There is also another application called Voice Commands. It's likely no one has responded because they couldn't figure out exactly what your questions was.
Since I don't know either, which of these you are trying to use, I'll comment on all three.
I don't have a problem getting either Google Voice or Voice Commands to find my contacts.
Google Voice uses the contacts off of your Gmail account. In order it to find the contacts, you have to have voice and Gmail use the same login. The Gmail account also has to be the primary account on your phone. Of note: The sync of contacts to your gmail account doesn't work on the DroidX. If a contact is coming from Faceback, it will auto link to the same gmail contact, but it will not auto add to gmail. There's a bunch of complaints about this on the Motorola forum.
Voice search is hit or miss on locating my contacts. It always tries to search the web. Perhaps this is what your trying to use to find contacts on your phone.