It's harder to be corrupt if you have to argue technically why your decisions will improve the economy.

Engineers and Scientists value the truth, whereas Lawyers value a convincing argument whether it is true or not. Think about their jobs: you can't convince reality you're right, but you can convince a jury.

I think you'd find it much harder to create feedback models of the economy which just happen to predict the best thing to do is to "Give Goldman Sachs a bonus to fix the economy", than it is to come up with some unprovable scare-mongering which terrifies the politicians into doing just that.

So yes, engineers or scientists would probably be more trustworthy running the economy as long as they stay true to the discipline.