Rugby league skills wouldn't translate into NFL skills, players such as Joey, Freddy, Locky couldn't utilise their skills to play. A halfback is comparable to a QB, but trying to compare their skills set is futile because the mechanics of throwing a NFL ball are so different to what they do on a rugby league field. On the other hand, guys like Folau and Inglis have those skills that could translate to nearly every football code - strong, fast, agile, good vertical, good hand eye. They are prototypical athletes.
ps. Webcke I still think Izzy would be a good RB, think Brandon Jacobs but you could easily put him in the slot as a reciever as well.