Could be, but I kind of think they want to throw all these guys out there and see which combination works. They have no certainties, but Elliott and Cook are coming off down years where they both looked like they are hitting the wall, Dowdle has not held up healthwise despite not really having to carry much of a load and who knows what Vaughn is going to become (other than Catch17).
I do think it's possible that he's not called up for the first game simply because of conditioning, and maybe if that happens and the backs do great without him, they'll wait.