If a model in 3DS Max uses a spline as a path and deformation reference, can I export the Max model with this spline somehow into a Unity project? Does Unity understand such animation? The model does not have bones, it only moves along a spline.
No - you can recreate with a spline IK, OR rig the model to a bone chain and deform using a number of techniques including morphs (but not other modifiers), or check into assets on the store. Best is Mega-fiers.