Are white bordered cards allowed in DCI sanctioned tournaments?
Yes, white bordered cards are legal.

From the Magic: The Gathering Tournament Rules (English version):


  Players may use any Authorized Game Cards from Magic: The Gathering
  expansions, core sets, special sets, supplements, and promotional
  printings. Authorized Game Cards are cards that, unaltered, meet the
  following conditions:


The card is genuine and published by Wizards of the Coast


  It is important to remember that fake Magic cards exist. Usually,
  these cards can be identified as fake under scrutiny. If these cards
  are found to be in use in a tournament, they should not continue to be
  used. Also, the player using the card may not realize that they are
  using fake cards, so aside from alerting them that they are using fake
  cards and informing them that they must replace them, we, as judges,
  should not take further action unless we believe they knew and were
  using such cards intentionally.
  
  Also, Tournament Officials do not have the legal authority to
  confiscate fake cards and should not attempt to do so. Stopping their
  use in the event is sufficient.


The card has a standard Magic back or is a double-faced card, or is a card that is part of a meld pair.


  Artist proofs are published by Wizards of the Coast, but do not have a
  standard Magic back. They are, therefore, not usable in tournament
  play.


The card does not have squared corners.


  Collectors’ Edition cards have black borders on the face, but square
  corners and a gold border on the back. These are not legal for
  tournament use. Also, uncut sheets of cards are sometimes cut for use.
  It is important that these cards have the same corners as all other
  cards.


The card has non-silver borders.


  Cards from Unglued and Unhinged have silver borders with a standard
  Magic back. These are not legal for play. Gold bordered cards also
  exist, though they do not have a standard Magic back.


The card is not a token card.


  Tokens are used to represent objects that don’t exist as normal Magic
  cards. While some official tokens exist, it is not required that they
  be used during tournament play.


The card is not damaged or modified in a way that might make it marked.


  Significantly creased cards can be distinguished from other cards in a
  deck, even sleeved. Also, altered cards may be thicker than the other
  cards in the deck, depending on the method used to alter the card. If
  any cards can be distinguished from the other cards in the deck
  without viewing its front face, then those cards are marked and not
  legal for tournament play.


The card is otherwise legal for the tournament as defined by the format.


  The cards being played in the deck must be printed in a set that is
  legal in the format, even if the printing being used is from an
  otherwise illegal set. For example, it is okay to use the Stronghold
  printing of Mana Leak in Modern even though Stronghold is not a legal
  set for use in Modern.