I am developing for mobile and to make the game run on lower spec mobiles, I was only going to import bones/rig for the main character. There are other humanoid characters in the scene which do move about and are rigged already in my 3d app but since they wont be controlled in anyway by the player in the game, I just wanted to bake and import their animations alone without the bones. I know unity can handle blendshapes but I am more comfortable with rigs and also cos these characters are already rigged properly.
No. Your 3D model MUST have bones of some kind in order to tell the game engine how it should move. Bones also include optional scripts, ik chains, etc., in order to tell it how to move around. Think of it in real life - without bones your body could not move at all. Same concept here. :D