See the first FAQ entry on the Camouflage page: Q: Is it obligatory to declare that the ARO is delayed when waiting for the second Skill when a troop in Camouflage or Impersonation State is activated? A: Yes, it is obligatory.
Not quite sure that is the rules quote we're looking for. Thats just that the absence of delcaring an ARO doesn't automatically mean you are delaying.
Ok, sorry, I think the 'against the Marker' bit is the bit that he's after. Specifically, what locks the ARO declaration in to specifically be AGAINST the unit delayed. I personally think the original interpretation feels like the most sensible and correct one from a game point of view but i'd love to see an ironclad ruling reference it.
To expand on @ijw 's response : The camo state is basically irrelevant to the answer. The ARO has to be declared against the first skill of an order that has a possible ARO, so if a model can see the first movement then they have to ARO against that, and you only get one ARO per order. Imagine we're not talking about Joan and a Crocman, but we've got a machinist in Joan's spot and a regular fusilier in the Crocman's. I want the machinist to get across the gap so they can get to an objective unmolested, so I use the same combined order, only I have to spend a command token to do it(or maybe Joan is still there and just doing 2 idles out of line of fire) the fusilier is way out in the open and unquestionably triggers the ARO, so the ARO is declared for this order, the second skills are then declared, the machinist moves and the fusilier dodges/shoots/chances it. Now imagine the sniper is actually a hacker, it would be really nice if you could declare oblivion or overlord on the fusilier right? Only you can't because they're not a valid target for those. Now flip everything back to the original example, the camo marker triggers the ARO for the order, but the choice of ARO is restricted by the target, and the ARO is declared within those restrictions, or lost. If a reasonable explanation for this in the real world is required, the camo token/fusilier is something moving in the corner of the snipers eye, distracting them causing tunnel vision and allowing Joan/Machinist to sneak past. Now if you have a second reactive model that has line of fire to Joan/machinist's move but not to the camo token/fusilier the first ARO available to them is Joan's movement so you get an ARO on her as a normal roll that she'll have to trust her luck and armour to save her from the shot...
Except because its a camo marker you don't declare your ARO (this being a specific game turn referring to all aspects of your ARO including the target at a specific point in the turn order) because you have selected to delay any declaration (and as such have selected no target). If it wasn't a camo marker (as per your fusilier example) then it would work exactly as you describe. None of that is being denied. It is specifically that no one can point to a single rule that says that when you delay you get locked in to only being able to target that character later in the turn. Ultimately though I think it's looking largely like, "the rules don't say what happens and everyone just plays it this way". Which is obviously not ideal but so long as everyone agrees it works. So thanks for taking the time to respond (particularly IJW who I think has probably got quite frustrated at trying to answer my query by now).
The examples say you only declare ARO against and react against one trooper. The word 'trooper' is important imo as it includes Markers that represent a model as well as models.
Again, you have to declare that you are delaying your ARO against a marker, which means that you are 'using' your chance to ARO. And once you've declared that you're delaying, the rule is: However, if you choose to delay your ARO, you may only declare it if the Camouflage Marker revealed itself with its second Short Skill. If the Marker does not reveal itself, the reactive trooper loses his right to ARO. So whether or not your ARO is locked to that marker (which it is), the only way your delayed ARO can happen is if the marker reveals itself.