I say no to felony convictions for any reason and here's why.   
  
1.  You don't have to be a leader to participate in scouting.  He can still be very involved and contribute in a meaningful way and not be a leader.  Being a leader does not get the leader anything extra.  
  
2.  Unless you are willing to print a dossier of all leaders letting parents know that this one is a felon, you are withholding information from parents.   At this point parents are not expecting felons past or present to be a part of scout leadership.   
  
3.  What is an innocent mistake to you, turns into a lawsuit, when you don't consider the next Dad's felon record to be a innocent childhood prank.  What we consider to be innocent is relative to our own experiences; what WE want to be looked over in our own lives.   
  
You are treading on VERY thin ice.