DNA analysis and sequencing can provide a lot of useful information,
and may be able to answer some questions that are not obvious by
morphological criteria alone.  Particularly, it may be able to
demonstrate that two forms are quite similar genetically (and
therefore presumably closely related) even though they are quite
different morphologically - or, that two  morphologically similar
forms are actually not closely related.  But as far as separation of
species, subspecies, etc. is concerned, DNA studies don't provide
automatic answers.  In the final analysis, someone has to make a
decision as to how much genetic variation is necessary to separate
two species - just as someone has to decide how much morphologic
variation is necessary to separate two species.
Paul M.
Rhode Island, USA