If you modeled an object based on the way it looks in Smooth Preview mode (i.e. toggling between key 3 and key 5), then you have to tell VRay to render the smooth preview instead of the actual base polygon shapes if that's your intent. You can do that by checking the "Render viewport subdivision" box in Render Settings->VRay->Global options. That will render (globally) all geometry in smooth preview mode in the viewport exactly as they appear in the viewport:
You can also do it on an object by object basis by selecting the object and adding a VRay Attribute in the Attribute Editor (Ctrl + a) as below:
HTH,
Jack
Smooth Preview Render in VRay
Smooth Preview Render in VRay
The master of disaster!