Alex-
If they are agreeing to release their material under the GFDL they have the right to be cited as at least one of the five most major contributors to the article. it says this in the GFDL.
They are agreing to release it into the public domain, so that's not an issue.
While I'm talking to a lawyer -- a completely unreleated issue: Do you know whether the text of patent documents (i.e. the description of patent claims filed with the USPTO) is copyrighted or not? The USPTO offers these documents for free download, but I'm not sure if it would be legal for us to use extensive quotes (beyond fair use) from recently filed patents. I did a Google search but that's really difficult with only "patent" "copyright" and "public domain" as possible search words, as you can imagine ..
Regards,
Erik