1) In Diamond and Pearl, a Pokémon with No Guard can successfully hit an opponent's Pokémon that has used Protect or Detect, but only if the attacker uses a move with less than 100% accuracy; the lower the initial accuracy of the move is, the higher the chance of the move breaking through Protect/Detect. Thus, when used against Protect or Detect, moves like Swift and Aerial Ace will always be blocked. OHKO moves are exempted from this behavior; they will always miss. This was a bug, and was fixed in Platinum.
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2) It may, may not.
3) Again, it may, may not.
4) Yes. Golurk, Machop, Machoke, Golett.
5) Yes.
6) No. And Focus Energy does not guarantee Focus Punch a hit.