WINE goes to some length to avoid any reverse engineering of windows components and certainly any glimpse of the source code (such as the leaks which have happened over the years: if you have seen any of them then WINE does not want your code). They do this to avoid any accusations of their code being a derivative work. If you re-implement an open-source project on the same terms then it does not qualify as a derivative work. However if you look at the source code and use that to develop your new implementation, then that qualifies.