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.