Need for Speed 2 unleashed Limited Edition.

The saves should be compatible. Any DLC content you have on your account will appear the next time you log in from Shift 2. My impression is that the DLC content is always there, and the login just enables one or more "flags" in your saves to unlock the content. This is based on my experience. I started off with Shift 2 unleashed, but never logged in until I had completed all the events that didn't involve the DLC. I backed up my saves made during that time. I then logged in and got DLC notifications about the DLC cars and events that were unlocked. If I go back to one of my old saves, I don't have any DLC content. 

Now I have a separate issue in that EA forced a password change on my account, but Shift 2 no longer allows a player to re-enter a password if it's invalid, and the old password I used doesn't follow the new rules so I can't change it back. I'd have to go back to one of my old saves where I never logged in, log in with the new password to get the DLC, then I'd have to replay all the DLC events again to get back to where I was, but I've lost interest in redoing all of those events. However, this experience is why I believe the content is always there, and just needs to be unlocked by logging in. 

Side note - I have the Dr Pepper Camaro which was a limited time special sponsored deal. There are also two "loyalty" cars for owning certain prior NFS games, but I don't have either of those.