I don't know if, but you would have to share the vertices over the multiple sub-meshes (one vertex array for all sub-meshes). I don't know if Ogre makes a copy of that array or just sets a pointer to it, when you call SetMeshData().
no
it would be anyway rarely pertirnent (even uv, even normal...)
on the other hand, ogre allows to define common vertices for all submeshes, but PB does not integrate this feature