does ffg have the right to use forgeworld concepts in the rpg? i think it would be cool to see some of the great creatures and vehicles from books like the siege of vraks done up using the deathwatch and rogue trader rules.

Possibly, though possibly not. Remember that FFG are only allowed to cover the setting as it is in their own areas (Calixis, Koronus and Jericho Reach), so even if they were allowed to use it, it'd:

1) have to fit with the setting in the RPGs; and

2) would actually have to be written up and put in a book, and since FFG books are written well in advance of their being printed and released, it'd be close to 6 months/a year before something from a Forgeworld book that is out now would be in a RT book.

Doesn't mean we can't make up out own stats

Exactly. Just means that even if FFG is allowed to use them, they might not do, and even if they do, they wouldn't be out for a while. In the meantime, the vehicle rules allow you to fairly easily make your own tanks and the like

When I did my write-up of the Raven Guard I used some of the Forgeworld figures of that chapter as inspiration. Notably the more pronounced beak on the corvus helmets and the raven skull tokens.