Yeah there are at least two ways of doing this in the galaxy editor.
The first way is environmental (I forget exactly what it's called). The environmental effect allows you to deal damage from one unit to another.
The second way is to modify unit property: life. Then specify life = current - damage. The problem with this second route is that it doesn't allow you to assign kills directly. I'm sure less roundabout solutions will appear in the future (and maybe they already have).