“I would like to respond to the main question in the article and also
correct a couple of mistakes in the article.

I am not a lawyer, but I have spoken extensively with lawyers about
copyright questions. Presuming that the VistA software is in the
public domain, if you combine it with a GPL-covered program you must
release the combination *as a whole* under the GPL. Using the VistA
code in this way is allowed because public domain status permits
practically anything.

However, the specific code that was in the public domain remains in
the public domain. In other words, the fact that person A released
the VistA code in a GPL-covered combination does not stop person B
from using the VistA code in some other way.

You could even extract the VistA code from the GPL-covered combination
and use it as public domain material, as long as it really is the
unmodified VistA code. If you want to use the VistA code as public
domain material, the safest way is to get a copy of the original VistA
code, because if people have changed that code since, they don’t have
to put their changes in the public domain. Still, in principle, the
VistA code remains in the public domain even inside the GPL-covered
combination.

Another way of putting this is that the GPL is not “contagious”. The
GPL applies through inclusion, not through contact. It applies to the
combination because the combination (given the assumed scenario)
includes some code that was released under the GPL. But the VistA
code retains its own status, despite being in a combination with the
GPL-covered code.

The same conclusions would apply if, instead of the public domain
VistA code, we were talking about a module released under the X11
license.

There are other licenses that have different restrictions,
particularly with regard to commercial use of software such as the
FreeBSD License. The Free Software Foundation does not consider these
licenses to be ‘Free’ licenses.

Actually we do consider them free licenses. Both the original BSD
license, and the revised one preferred by the FreeBSD developers (and
adopted by Berkeley a couple of years ago) qualify as free software
licenses, like the X11 license. We have used code available under
these licenses as part of the GNU system since the 1980s.

These licenses are non-copyleft free software licenses. See
http://www.gnu.org/philosophy/categories.html for more information
about this and other categories of software, and see
http://www.gnu.org/philosophy/license-list.html for more information
about the status of specific licenses.