Stunna, I am thinking the same thing. I am thinking if I can make my turrets small without screwing up the animations, and then make them stick to surfaces, it would be possible. But there is of course still the problem they can't distinguish between multiplayer-type teams (ie. red, blue, etc.).
About putting ai into cyborg biped, no that is not possible. You need to have an actv that points to a biped and an actr (the "ai file"). To get the bots into the warthogs I simply used the empty actv slots that are in every seat of every vehicle. I did the same for ghosts.
I have smart turrets done (they kick my ass because as of now there is no way to kill or otherwise incapacite them), but I am going to play with the ai now and see what I can figure out about it. Possibly I am get them to distinguish between teams, but that remains to be seen.