I have a CNC machine that reads DXF files. Are you planning on getting any files of this type on your website?
All of the DXF (and DWG) files I have seen are 2D, and would be suitable for use in a water jet, laser cutter, or even in a mill, if it were running as a router.
Are there 3D DXF files?
I think you'd be able to use 3D formats like step, and iges with your CNC equipment, but the limitation may be the software driving it. If the software only reads DXF files.
What software, and what CNC machine is it? Maybe someone with experience related to it can post a few ideas.
The models on GrabCAD can pretty much be any type of CAD file (mostly 3D). you would need to determine the use. many users will upload the native file format as well as many other formats. you will need to determine if each model is suitable for your needs (3D printing, CNC machining, renders...). For models that you want to machine you will probably need to take a model you like and import into your CAM system and create your own g-code. or slice it yourself to 3D print. If you need help getting a specific model into a format you can use most users will be more then happy to help if you ask.