NPCs adhere to FA On limits at all times: dump ion mines, they stop dead in space; their thrusters burn continually, etc and so on. The argument of how they implement those limits is academic. For all practical intents and purposes, they are FA On.
In more than five years, about 7k hours of play, and 40-50k NPC kills, I cannot honestly say I've run into a non-bugged NPC that was doing something I could not do with FA On. The only possible exception is how fast they can cycle railguns...never any delay or inconsistency, they spam them flawlessly...however, this isn't super human really, just a little better than what I can do. And contrary to popular belief, even Elite NPCs can miss with railguns.
Yes, they have full control over all of their thruster axes, but so does anyone with two sticks, and even KBM users can fake this well enough for NPCs to not be at an advantage.
I know Ion Doncaster has some other thoughts on how NPCs execute thruster control, but I'm fairly certain he'd also agree that any distiction from our FA On is academic.