From what I read, it's preferred to have a Karaoke version, but if you only have a copy with the voice track they'll let you use it and they'll be turning on vocal dampening.
Songs are limited to two and a half minutes (TV version, or one verse and chorus) for the audition, and five minutes for the competition songs. Songs longer than these limits will be faded out when the limit is reached.
Reference:
http://www.kumoricon.com/?q=node/17
