It's pretty likely that your 2D-derived cutting uses straight and circular arc moves, both of which can be handled efficiently by the motion control software. It's non-circular curves, or lots of sharp corners, that give problems.

For most hobby users, the motion control software runs on a PC and in effect takes a gcode toolpath file and via some piece of electronic hardware (as simple as the PC parallel port through to dedicated external hardware modules of more or less sophistication) converts the gcode toolpath into the electrical signals that go to the machine. In your case, the motion control elements are built-in and effectively part of the machine although technically they are still there under the cover somewhere. And it's the parameters associated with that bit of the control system that you probably need to tweak.

Personally, I would think that STL is as good a format for transferring a model into vCarve as anything else - and there aren't a whole lot of other formats that vCarve can use anyway! So the things you can play with are mesh density and any related controls in Rhino that are used to generate the mesh. In my case, the mesh size came from the spacing used to probe the original but if you are generating the mesh within Rhino from a 3D model, then you might have more options. Not something with which I am familiar, I'm afraid.