I was under the impression an aux firing arc counts as an arc for all purposes like autothrusters, tactician, etc. I was sure this was in the FAQ, but they seem to have bundled this all into a general question in the latest FAQ and it doesn't really address this specific question. Is there a rule somewhere in the FAQ or rules reference I'm missing? Had this come up in a recent game and I went to the FAQ and just couldn't find it.

Listed under the entry for Outmaneuver:

The auxiliary firing arc of the Firespray-31 is a firing arc.

At the time of that original entry, the Firespray was the only ship with an auxiliary firing arc and numerous emails around that time confirmed that anything that was dependent on a firing arc (Tactician, Outmaneuver, etc) also included an auxiliary firing arc within their scope. Any other ships with auxiliary firing arcs fall into that category now also.

Note that this does include the special firing arc on the Ghost, even if it doesn't have a docked Phantom to make the arc "active".