I would guess so, yes. You can never prove that something is random, merely that it behaves randomly "enough". There are lots of testsuites[1][2] you can run that will test that a generator is uniform and doesn't follow any patterns or has any other statistical weaknesses, but you can never prove that something is fully random without knowing the process that generates those numbers. A statistically sound RNG might just output the digits of pi, which would be non-repeating, uniform and pass any randomness test, but if you knew which digit the RNG started from and how many it has output so far you can easily predict the next one. Likewise if you're given a large enough sample you can search the digits to figure out the state of the RNG.
[1]: dieharder: http://www.phy.duke.edu/~rgb/General/dieharder.php
[2]: http://csrc.nist.gov/publications/nistpubs/800-22-rev1a/SP80...