I'd draw a distinction here between Open Source and Free Software. As we all know from reading RMS's highly entertaining rants, Free Software is a moral philosophy. Software is Free if it obeys the four freedoms. "Dumped" code is certainly Free.
In contrast, as we all know from reading Torvalds & co's equally entertaining responses, Open Source isn't a moral philosophy; it's a very pragmatic development methodology. The point of Open Source is that, when you structure a community in certain ways, and give them a certain level of access to a code-base, good things happen.
Code dumps do not follow the Open Source methodology, hence they don't get the Open Source results. Calling them Open Source regardless is like saying you've used the Waterfall model because someone scribbled out a half-page spec a year ago. You may have ticked one of the boxes, but you certainly haven't gotten into the spirit of things.
As another example, OpenOffice under Sun was Free Software because you could download the source code, but it was about as far away from Open Source as it could get without a spaceship. As a result, the software basically worked but had lots of annoying long-term bugs that no-one at Sun cared enough about to fix.
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