Just to call this out more clearly. The latest White Dwarf arrived today, with a Broken Realms flashpoint. There's narrative and rules for the War for Tepok's Eye, which features Seraphon vs Chaos. Belakor is a main part of the story, but his new model is not featured. It's a regular or garden variety Slann Starmaster leading the Seraphon, and I haven't spotted any reference to Kroak after skimming the article this morning. This suggests although Seraphon are part of BR Belakor, Kroak himself might not be.