Ryan,
Not sure what you mean. DirectX isn't a 3D geometry format, It's an API based multi media interface for Windows. One part deals with 3D graphics in a similar way to OpenGL in as much as it provides tesselation based real time shading. This isn't a file format, it's an attribute of a file depending on what the application uses for rendering.
The tesselation in both OpenGL and DirectX are similar, triangles, but only exist as a dislay list in the file.
The closest 3D file formats, to an OpenGL or DirectX display list, would be VRML or STL.
Are you trying to create 3D objects for games ??? I think most games that allow this accept VRML.
Mark