As you can see, only the most indented task in that picture is in black, the rest are in grey, signifying that they are not yet available. You could mark off one of the parents as complete, which would have the effect of completing all of its children.
The indentation is done by OmniFocus, not by putting spaces in front. If you looked at that project in the context view, all of the names would be aligned at the left, as seen here:
In context view, projects and action groups follow their contained task, with the containing item becoming available after all of the contained items are completed.