Was satan a worship leader? I've heard it claimed that Satan was the worship leader for God's choir. I cannot find any scripture in the Bible that mentions Satan was in worship in heaven and was closest to God. What is the Biblical basis for this belief?
Based on Satan was a cherubim, then yes.

GotQuestions


  Cherubim/cherubs are angelic beings involved in the worship and praise
  of God.


Who is Satan?

Satan comes from Judaism; "Satan" is from the Hebrew word for "adversary." Satan was existed in the traditions of Judaism as the heavenly prosecutor in what Christians call the Old Testament long before the incarnation of the logos aka the birth of Jesus.

Job 1:6 NIV


  One day the angels came to present themselves before the Lord, and
  Satan also came with them.


Satan's origins are hinted at here:

Ezekiel 28:16 NIV


  Through your widespread trade you were filled with violence, and you
  sinned. So I drove you in disgrace from the mount of God, and I
  expelled you, guardian cherub, from among the fiery stones.


Power the cherubim

Isaiah 37:16 NIV


  Lord Almighty, the God of Israel, enthroned between the cherubim, you
  alone are God over all the kingdoms of the earth. You have made heaven
  and earth.


Here is a popular depiction of the order from Matthaeus (Matthäus) Merian the elder (1593-1650).


 Relationship to music 

Ezekiel 28:13 hints to his relationship to music (see pipes and timbrels)

Ezekiel 28:13 KJV


  Thou hast been in Eden the garden of God; every precious stone was thy
  covering, the sardius, topaz, and the diamond, the beryl, the onyx,
  and the jasper, the sapphire, the emerald, and the carbuncle, and
  gold: the workmanship of thy tabrets and of thy pipes was prepared in
  thee in the day that thou wast created.