Quick clarification though:  If you simply want to allow another user to create objects in a given directory then set the ACL on that specific directory.
I'm using the REST namespace interface.  When I create an object and give FULL_CONTROL to another user (the path is created automatically), the other user can access the object, but can't access the directory that the object is stored in, nor any other directory along the path. The second user cannot create another file in the same directory, although it can create versions of the original object (which, I suppose, are not in the namespace).  Is there some other way to create namespace objects so that the directory/path inherets the specified UserAcl?
How does UserAcl work for namespace paths?