I believe all of the gnostic gospels undermine the traditional New Testament gospels, which is why they have been hidden, ignored, labeled as forgeries, and so on. The Gnostic Gospels, and especially the Gnostic Gospel of Judas, show Jesus as more human and less omnipotent and sure of himself, they show women in more power and more important, and many other things which later editors did not want to be accepted as truth.
No, this gospel does not undermine the traditional New Testament gospels. Really though if someone believed it did, I would not argue with them, because someone's faith is all thiers, and there are so many religious beliefs no one person can have the correct opinion on something, its all in your faith.
The Gnostic gospels do not contradict or even undermine the traditional New Testament Christian gospels, providing that one does not take the latter documents literally. The Gnostic gospels fill out the meaning of the others and give them a context that is deeper and refers to the mystical and spiritual nature of the world.
Although most people aren't aware of it, the traditional four gospels are not the only recorded gospels. The original Gospel was Mark, followed shortly by Matthew in the mid first century. The authors are unknown and unverified. Although the later gospels of Luke and John are attributed to certain people, their authorship is also unverified. There were dozens of gospels in use by the 4th century when the Roman Emperor held a conference to decide Christian doctrine. At this conference a vote was taken for which books should be in the New Testament. Four gospels made the cut, the others were discarded by Roman Catholics. The four gospels we know today were decided by a vote. A vote conducted 300 years after Christ's death by men who never met Him or met a man who had met Him. I don't believe that a vote of men who did not know Christ personally could accurately decide which gospels were truth and which were fiction. Prove to me that Judas did not write Judas. Then, prove to me that John did write John. Then I may reconsider.
The only reason the traditional New Testament gospels are considered traditional is the fact that those are the books the Catholic Church opted to include in the New Testament. For earlier Christians the Gospel of Judas would have been no different than the ones included. The only known Coptic copy was carbon dated to around 280 AD and was obviously not written by Judas himself. This may be why it was left out, but rather or not it undermines the other gospels is up to each individual reader.