If I add vertices to the bones can the vertices be from different objects?
You could do it in two ways.
- You parent each object to a bone in the armature. The bone will then have full control over the object. No vertex groups will be created. That means no smooth bending.
- You parent each object to the whole armature and you create vertex groups with Armature -> Name Groups. Then you can fill in the vertices for the vertex groups. These do not need to be the whole mesh, so smooth bending and weight painting is possible.
Choose whatever suits your situation best.