The site says Momoa recently flew to London and screen tested for the role of Drax the Destroyer in Guardians of the Galaxy. Marvel was blown away, and made him an offer which is now being negotiated with Momoa's reps. Dave Bautista and Isaiah Mustafa were rumored for the gig just last month.
Now, it should be noted that THR has countered by saying Momoa has not been offered a deal. They say he's merely one of the guys who read for the part. Marvel may still choose him, though. I'd have to believe that all things considered, the final two would be Bautista and Momoa, with the latter clearly having an edge in terms of recognition and experience. I'd still go with Bautista, but Momoa's a good pick.
We'll find out the truth soon enough. Guardians of the Galaxy opens on August 1st 2014.