In Daniel 3:28-29 (RSV), after Shadrach, Meshach, and Abednego were miraculously delivered from the fiery furnace, King Nebuchadnezzar was amazed and declared:

"Blessed be the God of Shadrach, Meshach, and Abednego, who has sent his angel and delivered his servants, who trusted in him, and set at nought the king’s command, and yielded up their bodies rather than serve and worship any god except their own God. Therefore I make a decree, that any people, nation, or language that speaks anything against the God of Shadrach, Meshach, and Abednego shall be torn limb from limb, and their houses laid in ruins; for there is no other god who is able to deliver in this way.”

This shows that Nebuchadnezzar and his subjects acknowledged God's supreme power and ability to save, but there is no direct evidence that they completely forsook their gods or converted to worshipping the God of Israel.