I don't think the 'certified unix' moniker counts for very much at all. It is uncertain that any non-corporately maintained Linux distro could qualify (per the opengroup page) as the kernel is developed outside of the distro.

The BSD's on the other hand could probably apply as they are one system (kernel and userland) with one governing body. But I doubt they really care to play the corporate standard mark game. They are UNIX and have always been so.