Is Mr. S. N. Goenka's Vipassana Meditation a Buddhist tradition?
Goenka tradition seems to be most close to meditation instruction sourced directly from the Suttas. A course is divided into  parts:


Anapana - cultivation of Samadhis (1/3 of the length of the course)
Vipassana - cultivation of Panna (slightly less than 1/3 of the lenth of the course)
Metta - (1 or 2 days depending on the length of the course.)


Anapana closely follows that of the [Maha] Satipatthana / Kayagatasati Suttas.

In the Vipassana part, the main instruction is whatever the sensation contemplate its impermanence and be equanimous towards it. 


  Having fully understood all things, he knows whatever feelings there are, whether pleasant, painful
  or neither painful nor pleasant.
  
  As regards to those feelings,
  
  he dwells contemplating impermanence in them;
  
  he dwells contemplating dispassion [fading away of lust] in them;
  
  he dwells contemplating ending (of suffering) in them;
  
  he dwells contemplating letting go (of defilements).
  
  When he dwells contemplating impermanence in them, contemplating dispassion in them, contemplating
  ending in them, contemplating letting go,
  he does not cling to anything in the world.
  
  Not clinging, he is not agitated; being not agitated, he himself surely attains nirvana.
  
  He understands,
  "Birth is destroyed, the holy life has been lived, done what is to be done, there is no more for this state
  of being."


Pacalā Sutta

Similarly there many more Suttas which similar instructions re occur throughout the whole cannon. E.g.: Pahāna Sutta, Avijja Pahana Sutta 2, Dīgha,nakha Sutta, Sal,āyatana Vibhanga Sutta, Indriya Bhāvanā Sutta, Dhātu Vibhaṅga Sutta, Titth’ayatana Sutta


  Bhikshus, just as if a man were sitting covered from head to foot with a white cloth, so that there
  would be no part of his body to which the white cloth did not extend; even so, the monk sits, permeating
  the body with a pure, bright mind. There is no part of his entire body that is not pervaded by pure, bright
  mind. 


Kaya,gatā,sati Sutta

also


  so, too, a monk reviews this very body, wrapped in skin and full of various impurities, from the
  soles of the feet upwards and from the crown of the head downwards


Kaya,gatā,sati Sutta, Sati’patthāna Sutta


  As below, so above [upwards from the soles of the feet, and downwards from the tips of the hairs.]


Iddhi,pāda Vibhanga Sutta

This is similar in tone to the head to foot scanning technique.

In Buddhism, common term is letting go. The Suttas on Letting Go sheds more light on how to do it. They are: Pahāna Sutta and Avijja Pahana Sutta 2. This is the exact way that is being taught by S.N.Goenka.

Also an interesting read might be: The Ancient Roots of the U Ba Khin
Vipassanā Meditation by Ven. Analayo, which quotes some parallel in the Mahayana Tradition which you (@Bhumishu 米殊) are from I believe.

Instead of intellectually debating on whether the course is this or that why not take the course and clear you doubts. You can apply through: http://www.dhamma.org/en/index and course are conducted in many centres around the world. You can choose a location convenient to you.

What matters if the techniques works for you or not than is it this or that. So best is just try it.