The FSF also requires signing paperwork and assigning copyright for GNU code contributions.

Why? So they don't have to worry (as much) about copyright infringement and patent bombs. VMWare could also sell or commercialize it (and the FSF has legal standing to sue for violations).

This is common. Otherwise you get a mess of copyrighted code, and making it effectively impossible to determine who owns the copyright to what. Good luck if you ever want to change the license or give one person a special license.

You can use Project Harmony (http://harmonyagreements.org/) to generate one of these agreements for your own project. It's targeted at FOSS, and the licenses themselves are under CC-AT-3.0.

It's quite common when companies open-source stuff. Google does this too.

You give up all rights to your code after you contribute it. AFAIK if you give up all rights to your code, they could potentially change the project license without asking the copyright holders. IANAL.

That's basically correct, though I would hasten to point out that of course they can't change the license of any versions of the software that have already been released.