How is Samson a witness for the Lord? My choir is singing a spiritual called Witness for my Lord which tells several stories of men who proclaimed God in some manner or other:


Methuselah who lived a long life.
Daniel who survived the lion's den in defiance of the king.
Nicodemus who visited Jesus in the dead of night and learned that he needed to be born again through public baptism. 


But one of the verses stands out to me:


  You read in the Bible and you understand
  Samson was the strongest man.
  Samson went out at-a one time
  And he killed about a thousand of the Philistine. 
  Delilah fooled Samson, this-a we know
  For the Holy Bible tells us so.
  She shaved off his head just as clean as your hand
  And his strength became the same as any natural man.  


(There are other variations of this verse, but all assert that Samson was a witness on the basis of Delilah defeating his strength through trickery.)

How does the Samson story fit with the other examples and in what way is Samson a witness?
I would tell you, but I have not the time:


  Hebrews 11:32-38
  What more shall I say? I have not time to tell of Gideon, Barak, Samson, Jephthah, of David and Samuel and the prophets,
  who by faith conquered kingdoms, did what was righteous, obtained the promises; they closed the mouths of lions,
  put out raging fires, escaped the devouring sword; out of weakness they were made powerful, became strong in battle, and turned back foreign invaders.
  Women received back their dead through resurrection. Some were tortured and would not accept deliverance, in order to obtain a better resurrection.
  Others endured mockery, scourging, even chains and imprisonment.
  They were stoned, sawed in two, put to death at sword’s point; they went about in skins of sheep or goats, needy, afflicted, tormented.
  The world was not worthy of them. They wandered about in deserts and on mountains, in caves and in crevices in the earth.


The song isn't saying that Samson was a witness because he was fooled. It's just a very short story of Samson, followed by a chorus. The biblical reasoning would be more clear if the last line told of how he cried out to God and was made powerful again so that he could avenge himself by bringing down a temple, but the song already told of how he killed many enemies. 

It's telling a story and saying that Samson was a witness of some form. It's not being very specific, but then again it's supposed to be more lyrical than theological. It's praising God through the recollection and praise of certain good people.