If you just give him the FAC role without specifying targets using FAC engage, He should give you targets that he detects and see's. I normally try to use that route, however it seems to be broken in the last patch. I tried it in a mission with Panzertard and he as well seems to think something is wrong so it should be getting looked at. They also need to implement some sort of target prioritization. I've had the JTAC give me a target 2km away while a enemy group is beating the piss out of friendly armor. It seems that there is no way for it to prioritize based on threat level, it just gives you random groups or groups you specify using FAC Engage Advanced Waypoint Action.