Are you sure about this? I know what the documentation says, but IME the aggressor having a criminal timer seems to change things in that regard in a way that’s not properly documented. Isn’t the victim in a limited engagement with the gankers already by the mere fact of being attacked, regardless of whether he retaliates or not?
Moreover, even if things were as you say, not sure but I think the Orca would still be able to assist the victim without going suspect by attacking the gankers and putting himself in a limited engagement with them too that way, but I believe this isn’t even necessary when assisting someone that’s being illegally aggressed.
And again, as long as the Orca pilot has safety enabled (green) the Orca will never be in danger regardless. The worst that may happen with safety enabled is that the remote reps will fail to activate or will deactivate if they were active already, so no need to tell corp mates to set drone behaviour to passive for that reason.
That said, it has happened to me in very rare cases (maybe just once or twice out of many) that I was unable to remote rep a hauler being ganked, but I could never figure why. The hauler didn’t have ECM nor anything else fitted that could have been used to retaliate…