I think in cases like what Wine is trying to do (reimplement/reverse engineer) you want "clean" engineers, not "tainted" ones. So I think that having their devs look at the windows source code might be the last thing they want.
Compaq couldn't just copy IBM's BIOS to make their new machine guaranteed IBM compatible, this would be illegal, and easily proven by IBM.
Solution: Reverse-engineer IBM's BIOS. Compaq used two sets of programmers - one group analyzed the original code and made notes of exactly how it responded.
The second group took these notes, and wrote their own BIOS that performed exactly the same.
http://en.wikipedia.org/wiki/Clean_room_design