There are some states that will take back the guilty plea once one does probation and complete sentence requirements like California. I got a DUI and now I am close to getting approved again because my court disposition now says NOT GUILTY. However, there are some states that do not expunge DUI's like Virginia. Unfortunately, he will have to go back to the shadows and wait for another type of law since VA does not expunge DUI's, https://vacode.org/19.2-392.2/
USCIS will still see the guilty plea and deny. I'm sorry , but as an immigrant; one mistake can ruin your life in USA.
This doesn't mean he WON'T ever be legal. He can get married and purse that route or wait for the real DREAM ACT to pass or Imigration Reform, if they ever happen. As for DACA, he won't qualify. It is cut and dry.