There is a bigger issue between FSDT and Orbx. The fact that the Vector AEC config utility (Airport Elevation Correction) which scans your scenery.cfg file and auto adds it to ignore it if needed is not working anymore.
This doesn't have anything to do with FSDT, of course. It's just that the OrbX utility MUST be updated to support what is an official standard in the P3D SDK.
Every 3rd party utility that needs to read the scenery.cfg will have to be updated to read also sceneries added with the add-on.xml, otherwise it will going to have issues as soon as more and more developers will adopt the new standard.
They just need to read the C:\ProgramData\Lockheed Martin\Prepar3d v4\scenery_addon.xml file, and add those areas to the ones found in the scenery.cfg. It's a file the sim keep updated, which include the list of the areas added via the add-on.xml method, it's XML, so it's really easy to read.