DBI::Dumper is under the same terms as perl itself, namely the GPL or 
Artistic licenses.  For more information, please see:

  http://rt.cpan.org/Public/Bug/Display.html?id=27269

From the bug:

Subject: RE: [rt.cpan.org #27269] DBI::Dumper license?
Date:    Thu, 24 May 2007 10:58:37 -0500
To:      <bug-DBI-Dumper[...]rt.cpan.org>
From:   "Smith Warren - wasmit" <Warren.Smith[...]acxiom.com>

The license for DBI::Dumper is the same as perl. I will update the
POD with the next release to include this information.