I say yes -- it's the equivalent of using a parameter entity to define a content
model.
One can imagine an XSchema where the top-level element declarations themselves
are relatively useless but exist so that an XLink can refer to their content
models. This is a bit hacky, but it's the only way I can see to duplicate the
horiz.model and vert.model entities in John Cowan's Itsy B
Bitsy Teeny Weeny Simple Hypertext DTD.