Besides the names, I don't see anything Slavic about them. Few people actually said anything. Anyone can say nonsense (just for the sake of it or to flatter the Slavs), even the producer, but that doesn't make it true. I wonder, are the other factions fighting against orcs, demons, etc., or are only the Griffins fighting, while everyone else attacks them specifically in the center? They could have told stories about others in Heroes 6, although instead of Griffins, they probably have wolves, bulls, and all the other creatures mentioned in their names, but they would look silly in battle, which is why they aren't there.