“Any contributions to core server code or patches need to have a Contributor Agreement.” does not make sense (:
Take a look at http://creativecommons.org/licenses/publicdomain/ and tell me why you can’t accept Public Domain contributions. I’ll quote the last lines so you don’t need to read the full license: “Dedicator recognizes that, once placed in the public domain, the Work may be freely reproduced, distributed, transmitted, used, modified, built upon, or otherwise exploited by anyone for any purpose, commercial or non-commercial, and in any way, including by methods that have not yet been invented or conceived.” Especially for the diff of a patch this makes it for the publisher more easy to supply the patch to you instead of downloading, printing, signing and faxing the Contributor Agreement to you.
And I may quote http://www.igniterealtime.org/builds/openfire/docs/latest/documentation/plugin-d ev-guide.html
"What license agreement are plugins subject to?
Because Openfire is released under the Open Source GPL license, any plugins developed must also be released under the GPL or a compatible Open Source license if you distribute the plugins outside your organization. It is a violation of the license agreement to create plugins for distribution that are not Open Source. Please visit Jive Software if you need different licensing terms for Openfire, including the right to create commercial plugins."
One could add a “Who owns the copyright?” section with the answer from above.