will there be hero units for every races(in campaign mode)?
Short answer: To a limited extent.
In regular campaign modes, there will not be heroes, simply because the gameplay of S.A.D. does not allow different types of units being used at the same time. THIS MIGHT CHANGE:
If time allows, I might make the game so that you can use a hero unit (or a group of hero units) as your "group of units." Risky, because if the heroes die, you lose.
For sure, though, there will be a few "combat missions" where you can use only one unit to do all of your dirty work, and you lose the game if that unit dies. In this case, the unit is a hero unit controlled by a particular character.