Checkmate legal here?

Imagine the following hypotheretical situation:

White play 1 Rf1 (for whatever reason), but to his horror he notices that he could have given mate in one and as quickly as lightning he puts his king on g1. The arbiter has seen the incident and obliges White to make a move with his rook, whereupon the latter gratefully plays 1 Rh8#.

What does FIDE rules states about this incident?

The arbiter made a mistake once the move is complete you can't take it back. The decision would have to be disputed and the game put on hold until a tournament director that knows what they are doing comes along. 

Yet another reason to take meticulous notes (not that you don't already)...

Imagine white play 1. Rf1 (without pressing the clock) and at the very last moment notices the possibility of checkmate in one (1. Rh8#). To revert the move he places his king on g1 (presses the clock) on purpose so the move gets reverted due to illegal castling. 

Is this castling loophole addresses in FIDE rules?

http://www.fide.com/component/handbook/?id=171&view=article

Articles 7.4-7.6

FIDE does not mention anything regarding this exploit of illegal castling.

As the rules ordain if you castle with your rook first both pieces shall be reverted to the previous squares and the rook is obliged to move.

Actually the rule that applies here is 4.4b: if you first touch Rook and only later King, you are not allowed to castle, but must move the Rook (because it was touched first, as 4.3a prescribes). To castle you must touch the King first.

No, you must touch the king first to castle. If you move Rf1, then lift your hand to move your king to g1, you've completed the move Rf1 and hence can no longer castle. It doesn't matter whether you touch other pieces after the move's been made.

I'm sure you can touch and move both at the same time. If there's no rule forbidding it, then it's legal.

FIDE rules indicates you can win that position if you perform the sequence flawlessly.

1. White plays 1. Rf1 for whatever reason and don't press the clock.

2. At the time he put his rook on f1 he discovers the mate on h8 and quickly put his king on g1 on purpose and presses the clock. 

3. The move gets reverted due to illegal castling. 

4. Rh8 checkmate.

It only works over-the-board and it's more like loophole exploit seemingly.

The only way this scenario can work is if Rf1 is played but hand not release the piece then as Rook lands on f1 you simultaneously move the King to g1 holding both pieces in your hand and swap them around. Your opponent has to claim the illegal move (the arbiter can't do it) only then will you be able to play the Rh8 move

The way I interpreted step 3 is that the rook must stay on f1. The arbiter should tell White that he is required to play Rf1.

Good someone understod the whole idea 

"The only way this scenario can work is if Rf1 is played but hand not release the piece then as Rook lands on f1 you simultaneously move the King to g1 holding both pieces in your hand and swap them around. Your opponent has to claim the illegal move (the arbiter can't do it) only then will you be able to play the Rh8 move"

Two hand castling is prohibited by FIDE so the move shall be reverted. 

So apparently this loophole is not working due to opponent will obviously not claim the move to get reverted. 

Conclusion: it will not work in practise unless your opponent like to lose, or something than worsen his position.  

Stop spamming and rather write something constructive instead 

What else would you expect from a spammer?

"BlunderfulPlayer"

More spam obviously! - golden rule broken (never feed the troll)

You probably shouldn't try that in the open section of OTB were generally players know the rules.