You should probably use the EvPoint method rather than EvaluatePoint. EvPoint will take the parameter along the curve, then the 3d point to output the location to.
Its going to be fairly useless for you here in GH. Basically, its a reference to an object, not the object itself. Its used within classes like MRhinoGetObject as a way to "hold on to" an object yet not have the overhead of having another copy of that object in memory. AFAI can tell, the class is really only there so MRhinoObjRef can derive from it. I haven't really seen it pop up from within the OpenNurbs SDK yet.