Actually, the engine will only determine shot attempts if everyone is set to "0." In my experience, the guys who are set to "0" will only shoot on put-backs or breakaways. I generally set my poorest shooters to "1" though -- I want to at least give them a chance at glory.
I'm a little confused by your post, deacon. It's very easy to make a guard a pass-first, shoot-rarely type of guy. It's all the in the distro. Bringing a scorer off the bench is slightly more complicated, but coach_ms laid out a nice plan. The thing you want to be careful of is to put too much distro on one back-up player when the rest his teammates on the court have very little. In coach_ms's plan, the SG will take half the shots when he's the only back-up player on the court. But let's say the other back-ups are in with the SG and have distros of 2, 1, 1 and 1. Now the SG has 25 of 30 available distro and he'll be taking 5/6th of the shots. When one player's gunning like that their effectiveness tends to go way down.
So you do need to do a little experimentation to find a nice ratio for your scorer -- but I haven't seen any negative effect in FG% when one player has half the distro.