Idle is never a valid ARO. If you have an ARO you may delay it (by stating 'I delay my ARO against that Marker'). Because a Camo Marker isn't a valid target of Hacking then if a Camo Marker activates inside a Hackers Hacking Area but outside ZOC an ARO isn't generated so there's no need to delay anything.
But if the Camo marker reveals itself in his second short order (shooting f.e.), then the enemy hacker gets an ARO - so he has to delay first?
Nope. Doesn't need to delay at all, because there is no valid ARO to delay declaration of. So: 3. Camo marker walks into apparent ZOC of a Repeater 4. No AROs 5. Camo reveals as a Zulu Cobra KHD and Redrums the Interventor 6. Spektr KHD drops out of HD and Skullbusters the ZC. Interventor declares Breakwater.