According to Mormons, Jesus is Jehovah in OT. Therefore do they view all the occurrences of the Tetragrammaton as referring to Jesus? Lesson 5 in the "Jesus Christ and the Everlasting Gospel Teacher Manual" (link) has the title Jesus Christ Was Jehovah of the Old Testament.

In the introduction this lesson says that:


  In testifying of the Savior Jesus Christ, modern prophets have
  declared: “He was the Great Jehovah of the Old Testament” (“The Living
  Christ: The Testimony of the Apostles,” Ensign or Liahona, Apr. 2000,
  2). Jesus Christ, as Jehovah, established Heavenly Father’s
  everlasting gospel on the earth in every dispensation of time in order
  to gather in every one of God’s children who were lost.


According to the LDS are all occurrences of the Tetragrammaton in Old Testament then references to Jesus?
This is correct, and easily supported by the Bible, particularly the writings of John.


John chapter 1 states that "all things were made by him; and without him was not any thing made that was made." So we see that Jehovah, the creator of the world, is Jesus.
In John 14:6, Jesus says that "no man cometh unto the Father but by me," and 1 John 2: 1 calls Jesus our "advocate with the Father", showing that interactions between man and God -- such as those experienced by Old Testament prophets -- are with Jesus, rather than with the Father.
In Isaiah 44:6, the LORD (tegragrammaton) states "I am the first and I am the last"; Jesus similarly identifies himself as "the First and the Last" in Revelation 22:13.  (See verse 16 to clear up any ambiguity as to the identity of the speaker here.)
In the end of John chapter 8, Jesus angered the local Jews by equating himself with "I AM," the name by which Jehovah identified himself to Moses in Exodus chapter 3.  In verse 14 the being in the burning bush calls himself I AM, and in verse 15 he calls himself the tegragrammaton.


So we see that Jehovah is identified quite clearly with Jesus, rather than with the Father, and that interaction between mankind and deity occurs exclusively through the mediation of the Son.  LDS doctrine holds that this is a consequence of the Fall, separating mankind from the Father.

Interestingly enough, the first chapters of Genesis use a rather unique term for deity: Jehovah Elohim, translated to English as "The LORD God", created the world and interacted with Adam and Eve in the garden of Eden, and then ended up casting them out after they partook of the forbidden fruit.  From that point on, starting in the next chapter, the God they interact with is simply Jehovah.  LDS doctrine holds that Elohim ("God" in Hebrew) refers to the Father when used as a personal name, (the term is also used as a generic word for any god, including the false gods of other peoples,) and that these early chapters, before the Fall, spoke of the Father and the Son together creating the world and interacting with Adam and Eve, but after being driven out of Eden, the privilege of direct communion with the Father was lost.