The reason OSI didn't approve it is because CC0 does not grant you a patent license. So you if you use CC0 "licensed" code in your own projects, you are free t

The reason OSI didn't approve it is because CC0 does not grant you a patent license. So you if you use CC0 "licensed" code in your own projects, you are free to do anything with such code from a copyright perspective -- but the author of the CC0'ed code has explicitly not given you a patent license for that work.