A subentry is a special kind of entry immediately subordinate to
an administrative point. It contains attributes that pertain to
a subtree (or subtree refinement) associated with its
administrative point. The subentries and their administrative
point are part of the same naming context.
A single subentry may serve all or several aspects of
administrative authority. Alternatively, a specific aspect of
administrative authority may be handled through one or more of
its own subentries."
Here is a description about subentries in ADS : http://directory.apache.org/apacheds/1.0/the-administrative-model.html
Basically, no way to get a DN pointing to 2 entries. At least in ADS, and I don't see how it can be possible in any other ldap server (or I would be surprised).
Again, the fact that other ldap server define a DIT with an empty DN is breaking LDAP specs. I think they allow this as a workaround to a problem with Exchange servs which kind of allow this. But you will have to find me the place in the RFC where this is explicitely allowed, when I exposed the place where it is said that it's the rootDSE DN ...
Of course, I can be plain wrong, and in this case, we will have to reconsider a lot of things in ADS, but that's another story