Technically it's not prohibited, but some OMV/DMV offices are in prohibited buildings. So the simple answer is no. The complicated answer is, well you can, but only if it's a standalone OMV/DMV like the random locations in strip malls.
Unless the office is located in a building prohibited by R.S. 40:1379.3 or has posted signs, I believe you can carry. However, I'm just a dude on the interwebs who has not yet found a statute proving otherwise.
That "where is it located" thing caught me once. My wife didn't want to go downtown in NOLA by herself when she had to go pick up some specific tax forms, and we walked into the building, took the elevator up, down the hall, and entered the enclosed office which, because the space was being leased by the Federal Government for various agencies, was subject to their regulations which prohibited the firearm which I was carrying. Easy deal, wait in hallway, but crap like that sure is aggravating.
The office in Shreveport is located in an old ice skating building. It also has a parish sheriff's deputy on site for whatever reason. The building also houses the Child Support offices.
I was there yesterday and the place was packed. There is a lot of loitering in the parking lot but I never heard of any problems there.
My sidearm remained in my vehicle but I always have concern about the security of it being in my vehicle.
Nothing I read in the rules say it would be off limits but that is my private interpretation. I also know laws only apply to certain people. What one can get a pass on, there will be others spending a year behind bars.
To enter the one in Terry Town/Harrahan on the West Bank you need to go through a medal detector....plus there are signs everywhere that say 'no guns' so that one would be a no.