I downloaded the free DLC and I'm going to play with my friend over Xbox Live who has the premium DLC. I was wondering if I am still able to get the DLC Achievements if I play with him or not (like in Crackdown).
You can't even access the full dlc with the free version. All the free version gets you are a couple pieces of equipment and an advertisement to buy the premium dlc. You can't actually travel to knothole.