Earlier quoted context omitted.
I don't work on emulators, but I do work on Wine. We explicitly forbid any contributions from anyone who has seen any Microsoft source code. The risk of introducing work derived from code owned by Microsoft is too high. I don't know how strict emulator authors are about this--they're non-commercial and so have less at stake than we do--but if I were an emulator author, I would cut ties with anyone known to have looke…
The whole reason emulators are legal and ROMs aren't is because emulators are original work not owned by the console developer. Except that people need ROMs to test emulators with. Just like the old saying that it's impossible to actually start "from scratch", at some point everything is a derivative work of everything else; it just has to be far enough away to not attract legal attention.
[1] At least for now; burn in Hell, Oracle.