KPHP implements some mysqli_…() functions, that can be called MySQL support somehow.
But, at VK.com, we use a special db-proxy layer between KPHP and MySQL databases. It is a daemon running on every server: it manages connections, performs master-replica routing, handles access rights.
As a result, KPHP just skips credentials passed to mysqli_connect(). Moreover, MySQL connection can only be opened to localhost with unix socket.
So, MySQL support for “real-world usage” is also still to be done.