I'll confirm this. I have two keyless entry remotes, but I (almost) always use a plain metal key to both lock and unlock the truck and to start it. It works fine regardless of whether or not there is a fob even nearby.

 

My first D2 did not have a fob, and the single key that came with it was just flat bare metal. Never had a problem with the alarm or immobiliser.
My current one has fobs but I also have plain keys that work just fine.

(Side note -- if you're going to use a key to lock/unlock the vehicle, make sure you upgrade the lock pin inside the door so that it doesn't break and leave you stranded.)