I haven't been able to find a pic or a reference to that specific vehicle yet, but I have found some references to "Übungspanzer" in the Bundeswehr (BW). From what I gather (all the sites were in German and I was having flashbacks to my German language course and the disappointment of my teacher that all I would be able to do was order beer and unsuccessfully chat up women) when the BW was first constituted they had difficulty in keeping a sufficient percentage of their tracked armored vehicles available for training/exercise partially due to a lack of trained (and in uniform) mechanics. One of their solutions was "Übungspanzer auf Radfahrzeuggestell" (exercise 'armoured' vehicles on wheeled chassis) or "panzerattrappen" (dummy tanks/armoured vehcles). Less maintenance required. According to one source there were two types "Kampfpanzer" und ""Schützenpanzer"; there 'might' have been more variants and there 'may' have been a direct visual correlation between the exercise vehicles and the actual armoured vehs they represented. They were built on a Unimog chassis. Most of the references indicate thay were used in the late 50s - early 60s and one poster on another forum said he had pics of his father with such vehicles during his service in the BW 1964-1965.
So if I want to really disappoint my former German teacher, the picture you provided may be an "Übungsschützenpanzer".
I was able to find (on an official BW website) a photo of a "kampfpanzer type" with the caption "Übungspanzer der Bundeswehr auf Lkw-Fahrgestell, Ende der 50er Jahre".
I was going to reserve that photo for a future challenge, but, what the hell!.
Edited to add:
May have found an official designation:
Übungsschützenpanzer (UebSPz) mit Panzer-Attrappenaufbau HS 30
and the tank variant Übungskampfpanzer (UebKPz) mit Panzer-Attrappenaufbau M 47
Built on a Unimog: Lkw 1,5t gl (Bw) - Mercedes-Benz Typ U-404 S