Custom local map

You can only use maps that are made in Maps Made Easy natively. If you host your created GeoTiff with Mapbox or ArcGIS you would be able to display it within Map Pilot Pro using a 3rd party datasource in the Settings. This would be a URL like this:

https://services.arcgisonline.com/arcgis/rest/services/World_Imagery/MapServer

Or a valid Mapbox Style URL.