Ive been planning to use it for a level editor myself, my plan is to write an exporter to send the scene data to an XML file, which could then be parsed to load and manipulate the objects in dbpro.
It really needs a separate export from the .x, as the format doesn't support such custom properties in anyway which could be auto handled by load object. You could append them to the file, but would need to open to read and parse the info out manually anyways.
Possibly an almost ready made solution: You might look at exporting the overall scene with the .x3d format. Dbpro can't load from it directly, but it is based in XML which can be handled with plugins and it includes more scene centric info than the .x it does also include a collision enabled tag if physics are set to an object in blender, though it does not seem to include custom user defined properties atm.
Anyways I guess my point is different exporters will best serve different jobs object vs scene, and it's going to need a specialized map loader within dbpro to import the scene however it gets out of blender
