Flowgraphs and AI do work in Multiplayer, there are settings in the flowgraph editor that deal with multiplayer.
Of course, the problem is, what exactly does work. Stuff that effect weapon loadouts and the like do work, as well as moving lights and such.
AI works, because what are the turrets?
They are AI Archetype Entities.
Granted, they are static. I think the issue lies in the fact that AI navigation nodes do not work online, which means all AI is pretty much useless unless it's static... like turrets.