1) What is the rule regarding whether iterative attacks can gain the benefit of sneak attack damage? I'd prefer cites if possible,
From the SRD:
SRD said:
Sneak Attack: If a rogue can catch an opponent when he is unable to defend himself effectively from her attack, she can strike a vital spot for extra damage. The rogue’s attack deals extra damage any time her target would be denied a Dexterity bonus to AC (whether the target actually has a Dexterity bonus or not), or when the rogue flanks her target. This extra damage is 1d6 at 1st level, and it increases by 1d6 every two rogue levels thereafter. Should the rogue score a critical hit with a sneak attack, this extra damage is not multiplied.
With respect to any attacks, check the enabling conditions for a sneak attack: target denied Dex bonus or flanked. When the rogue takes his first of any number of iterative attacks, does either condition apply? If so, sneak attack damage applies. When the rogue takes his second iterative attack, does either condition apply? If so, sneak damage applies. etc. Key to the interpretation is "any time" -
any time the conditions apply, whether the first in an iterative attack sequence or the last or the middle. If the condition applies, the sneak attack is a go.
It's possible that the loss of Dex bonus might change from one iterative to another. Invisible rogue causes target to lose Dex bonus, after first attack rogue becomes visible, thus no longer causing target to lose Dex bonus is a very common interpretation of those rules. Flanking usually persists throughout the iterative attacks unless some other ability intervenes to move the target out of flank.
2) Same question for scout skirmish damage and ninja sudden strike damage.
The scout's skirmish damage relies on the scout having moved 10 feet or more during the turn (Complete Adventurer p 12). Since that's a move action, full attacks are not permitted and so no iterative attacks can be made. At least not without some other funky power being called on that would allow more movement while still getting in a full attack.
The ninja's sudden strike ability does not apply during flanking but only if the target is denied a Dex bonus (Complete Adventurer p 8). Like the rogue sneak attack above, consult the target's status. If he's still denied his Dex bonus, then each iterative attack can get the sudden strike damage.
3) Are there any other SA variants?
I have no idea.