Say an arverni player is targetting a roman group consisting of hidden auxilia and an allied tribe. Is the roman player even a valid target to initiate battle with?
Im coming from Cuba Libre, so intuitively it seems that since the auxilia are hidden, they are immune from battle until they are revealed. Is this how it works here too?
In Falling Sky you don't need to reveal (i.e., Activate in CL terms) warbands to attack them. Being hidden is useful for a number of things such as harassing enemy March and several Commands (Ops) and Special Abilities. If you attack the Romans and they don't retreat they will become revealed after the fight anyway.
It's also worth noting that in the ancient world it's easier to get hidden once revealed. Pieces that March have the opportunity to flip to hidden, even if just Marching in place.