[JKT]

You need to save a new New Document Template with inches set as the ruler. In OmniOutliner Pro, this is easy - in Preferences>General click the Edit New Document Template button and set up things the way you want them to be, including the ruler measurements, then save it. From now on, new documents will open from that template. In OmniOutliner (non-Pro) you have to use a workaround and I forget what it is.