Im not so sure, there are apparently 2 NRL clubs interested. If Newcastle don't bid for him then they have lost the plot as he is miles better than Mamao.
He would also be an improvement for the Bulldogs (his best option) the eels and possibly the Dragons or Souths

He wouldnt get a gig at the Dragons with Dugan at Fullback already. I know he has played a few positions like centre to help the team out but Dugan is the Dragons best fullback. Souths again cant see it, they have Inglis there who recently was playing 6 but again I think fullback is his position also they have Alex Johnston who wants to play fullback. I just cant see a gig for Hardaker in the NRL.

Storm - Slater and Munster - No
Panthers - Moylan - No
Titan - Hayne - No
Brisbane - Boyd - No
Raiders - Wighton - No
Cowboys - Lachlin - No
Sharks - Barba - No
Tigers - Tedeseco - No
Warriors - Sheck - No
Sea Eagles - Trobojevic - No
Roosters - Just signed Gordon - No

That leaves the Bulldogs may be an option or even Parra but could they afford the fee. Knights yes but you would be stupid to sign for them!

Impressed by your NRL knowledge.

Some coaches can turn players around. Kear, Smith and Powell are 3 who have shown they can, but they've also got rid eg Gleason from Warrington

Looking at this list makes you realise the depth in the NRL at fullback is ridiculous, I'd say greater than any other position! Bulldogs have Hopoate who's a good player and as far as I know they're happy with him (despite the controversy about him not playing on Sundays).

I don't think signing for Newcastle would be as bad as you say, clubs in the NRL only tend to be very bad for a couple of years at most! Roosters went from wooden spoon in 2009 to Grand Finalists in 2010 and winners in 2013. Cronulla went from wooden spooners in 2014 to Grand Final winners in 2016. Newcastle have got a young squad and a good coach, and some good young players in their reserve team I believe. However, they would be better teaching a young talented outside back to play fullback rather than put Hardaker there IMO.

Bulldogs also have Morris, who's a superb full back.

Based on this year's performances no NRL side would pay much for Hardaker. Having said that the Knights are desperate for players, and Brown has seen a better version of Hardaker previosuly. How much of his averageness this year in the NRL was down to messing around at Leeds most of the season (one try in 17 games before he left sums it up) we don't know. With a proper off-season and some focus he might end up a better player - the snub from Wayne Bennett may make him realise how far he's dropped off the pace and how much work he needs to do. Given his past, I wouldn't bet my house on it though.