Pages 121-3 of Lost and the Damned tell the tale of Lothar Bubonicus who does indeed rise to become a Daemon Prince. There is no mention of him being granted a Daemon world only that he enters Nurgles realm.
Page 162 features the line \"Another world has boiling lakes of blood from which spheres of fire float into the sky and spread their light across the firmament - the ruler of this world is the Daemon Prince Bubonicus, formerly a mortal champion of Nurgle on one of the myriad lost worlds in the galaxy.\" Again no specifics, it\'s left purposefully vague so you can infer what you wish from it. It doesn\'t categorically say that this is the same Bubonicus and lets face it it\'s not the first time GW has recycled names. Most of the named characters in the new Daemon books are usable in both systems.
It would be a massive headache for GW to place the Warhammer world into the 40k background as they would have to explain amongst other things; why Elves don\'t need Soulstones, why Orcs don\'t spontaneously manifest the ability to create technology, why Dwarves, Ogres and Halflings were seeded by the Old Ones rather than evolving as abhumans as they do in 40k. Also if the twin tailed comet was Sigmars gene vat falling to earth why has it been seen several times afterwards? and the most important question of all why does he have a belly button?