For what it's worth I figured I would post to clarify a few things. Been following the NRL for 4 years now and grew up playing football from peewee through high school into college.
I haven't followed the NFL in over a decade and for anybody who does if you get a chance check out NCAA football, bigger crowds, better atmosphere, higher intensity/desire and more unpredictable.
As far as Hayne goes he's gonna be up against it. If the 4.7 40 number is correct he's gonna struggle. He's built like a strong safety but runs like an ILB/DE. To put into perspective J Clowney who went 1st overall ran a 4.55 40 and he the same size as G Burgess, 6'5" 265.
He might be able to make it as a KR/PR but w/ roster limits he has to offer more. He also has to play as a gunner and work really hard at becoming a #5 WR(slot).
He doesn't have the size to play outside at WR, think Edrick Lee, and he wouldn't make it at running back. Most NFL backs are in the mold of Michael Jennings and the easiest thing a running back does is run the ball.
Blitz pickup, releasing to the flat, finding the soft spot in the zone etc.. takes a lot of practice and hundreds or hours of film study.
IMO he will be back in the NRL for 2016. The biggest thing I would worry about is he hasn't learned how to protect himself, namely his legs. In football yards/meters are much more of a premium. The no wrapping up to stop the offload it's about stopping forward progress i.e. running full speed and diving at the knees. There's a reason why the average NFL running back only plays 2.5 years.