Seraphon are here in the Hammerhal Herald and in classic tabloid fashion it asks the real questions. You can find the Hammerhal Herald right here!
I am pretty sure we are actually both. Or can be. Slann can pull Seraphon out of thin air and magic if need be, but they are also created in spawning pools and they probably prefer casting spells instead of remembering their troops into existence. I think the newer fluff texts and the ingame mechanics fit that explanation well. ...and I admit I also like how that explanation fits to my own fluff.