Notetab Standard and Notetab Pro have an Outliner of sorts. It basically consists of a flat list of topics which does not seem to allow different levels of notes.
You can however emulate different outline levels quite easily. Go to View|Options|Outline and select "Show heading in Outliner." You will now see the headings at the top of the topics. Adding a space (or two) at the front of the heading will actually show the text as if it were the child of the previous topic. Two (or four) spaces make it appear like the child of the child, etc.
It's not easy to keep track of the spaces, but it will work.
1. Actually, you do not have to make the headings visible. You can also add the spaces directly when you enter the topic name. But I find it easier to keep track of them with the headings visible in the topic.