Air France actually has its own ticket counter next to Delta's, but their operations seem to be pretty well blended otherwise: I got a DL boarding pass from the AF agent for my AF flight, and was sent to the (very nice) DL lounge. I was very impressed with AF/DL service at LAX.

Two hours in advance should be plenty of time to check in and clear security for a mid-week midnight flight (you'll probably end up with an hour to kill at the terminal), but traffic in LA is bizarre and unpredictable, so try to find out the state of the freeways you'll be taking (if any) at around 8 or 9 pm. AM 980 has traffic every ten minutes.

If you just go up to Santa Monica for your layover, you won't get caught in any terrible traffic. And it's one of the nicer parts of town, with a decent beach, good shopping and restaurants, and great people-watching. A taxi ride won't cost a fortune, either.