As to your question about setting schemes to help sim stats, I really don't have a good answer for you. At this point I'm not really paying attention to stats as I'm focused on the way the game plays and how various players play. Its been said that the game doesn't seem to have a "soul", not much difference in how various teams and players play.
So far, I've found that we can get CPU controlled QBs & HBs to play more to their abilities and real life tendencies by assigning a certain player style in the coaches menu. We can also influence how a team plays by assigning certain play books and adjusting team schemes.
As an example, in one game I played the PIT. Roethlisberger was hurt and Gradkowski was the backup. He has a very week arm, so I set the team to a more run orientation and set the QB to WEST COAST. PIT ran the ball more and Gradkowski went for shorter underneath passes.
As for distributing HB carries, I don't see schemes as being able to affect that outside of having the scheme set to where a team runs more.
I've been trying to see if schemes have an affect on WR play as well as OL. To this point I haven't really seen anything I can say for sure as to OL play. I'm also trying to see what the effects are on DEF play. I have seen that if you set the DEF scheme to say ATTACKING 4-3 as opposed to BASE 4-3, teams will blitz more. Much more needed to see if there are any useful trends.