These are Lorgar's 'Blessed Sons' - aka daemon-possessed Word Bearers.

The Gal Vorbak of the 10th Host are a bit different from the 'old ones'. The 'new' Gal Vorbak are spirits of slain Word Bearers (the line between a 'spirit' and a 'daemon' is pretty academic). They take over the bodies of worthy hosts at the moment of death. The late Obel Gar was the first to rise.