Yes and no… While you can assign a material to certain vertices and they can then be selected that way, vertex groups, as used by Blender, are actually separate from the materials. So you can have vertices that have the same material, but are in different vertex groups. In fact, you could even have vertices that have different materials but are in the same vertex group. All a vertex group really is is a collection of vertices that are put together in a group and given a name. There are lots of ways that could then be used. As for the materials, the vertices that are assigned to a material are just so that Blender knows which materials to use with which vertices.
