Reference counting does not trace dead objects. Most of its activity is concerned with maintaining reference counts on live objects.
When a reference count hits zero, that's when refcounting begins to be concerned with a dead object; and that part of its operation corresponds to the sweep activity in garbage collection, not to the tracing of live objects.
It is not a dual to garbage collection concerned with its negative spaces; it's simply a less general (we could legitimately say lesser) garbage collection that doesn't deal with cycles on its own.
When a reference count hits zero, that's when refcounting begins to be concerned with a dead object; and that part of its operation corresponds to the sweep activity in garbage collection, not to the tracing of live objects.
It is not a dual to garbage collection concerned with its negative spaces; it's simply a less general (we could legitimately say lesser) garbage collection that doesn't deal with cycles on its own.