Cheops-ng: DFSG free or non-free?

["Wesley W. Terpstra" <terpstra@ito.tu-darmstadt.de>]

I have a package which has in the COPYING file this text:

Cheops is distributed under the terms of the GNU General Public License.
In addition, Adtran's name MAY NOT be removed from the product (or any
derivative work) and must be prominantly displayed in any "About" box,
documentation, product literature, etc. (BSD style).  In many cases,
written exceptions for this rule can be obtained by e-mailing the authors:
                                                                                
Brent Priddy (toopriddy@mailcity.com)

----
Then the standard GPL v2 follows.

I wanted to check whether this means the package is DFSG or not.
I know the advertizing clause in BSD is allowed, but GPL incompatible.

So, what does that mean for a package where the copyright holder distributes
the package with an extra clause and GPL? Can I redistribute it at all?

PS. Please CC me on replies as I am not subscribed.

-- 
Wesley W. Terpstra