Yes. Again, Google can do whatever it likes with its repositories. This is entirely unrelated to whether or not the software is proprietary.

Compare Google's practices here to Qt's[1], CMake's[2], or any other large open source project that is primarily maintained by a single company.

To be abundantly clear: I don't think this is a good way to run an open source project, but it is a legitimate way to run one. So long as the source code and standards (insofar as they exist) are themselves permissive, then the community details are just that.

[1]: https://wiki.qt.io/Qt_Contribution_Guidelines

[2]: https://github.com/Kitware/CMake/blob/master/CONTRIBUTING.rs...