About the publication requirements:
It would be good to ask if there are any paper documents that were signed during the conference, that would have historical value, if not, then just remove the notice.
About the copyright notice:
I have taken a look to:
http://openaccess.mpg.de/3515/Berliner_ErklaerungAnd there is a copyright notice at the bottom: "© 2003-2014, MAX-PLANCK-GESELLSCHAFT, MÜNCHEN"
The options are either to ask them to use a compatible license or send them a OTRS request
Regarding "no links":
That is easily solved, specially if you are uploading OA materials, then just link from your OA main page to the declaration as a related document.
Cheers,
Micru