The Rodenstock distributed camera lens production in later years was up-market of Zeiss Ikon - after the fifties, they only distributed large format, process and aerial/military lenses. In small and medium format, they supplied Kodak, Edixa, Polaroid and some more - but all I am aware of are Rodenstock branded, so they weren't really a OEM (where the customer would apply his own brand).
Rodenstock would have had the capacity to act as a Zeiss OEM, and did deal with them (Rodenstock was a large Schott optical glass customer). However, I have never seen solid arguments (like a contemporary document) for Rodenstock OEM lenses on Zeiss Ikon cameras - the reason usually given is that early on there was a Rodenstock BRANDED lens on one odd Zeiss Ikon camera earlier on. But as I said, that will have had political reasons, it was the last Dresden made body distributed by Stuttgart after Zeiss fell apart - and Rodenstock even branded a Zeiss design in that case (which makes it very special, and no OEM deal).
As Zeiss was the power centre in the West German optics industry, and notorious for integrating everything under their own corporate umbrella, down to manufacturing screws and casting glass, I think is outside their corporate structure and psychology that they should have outsourced lens productions for capacity reasons during the decline period of the German camera industry. If any, it might have been strategically driven support for one of their struggling optical glass customers (perhaps with the intention to embrace and take over, as they often had done throughout the 1920s, or maybe only as a stop-gap measure against declining demand for glass types used in camera lenses). If so, it might be difficult to find hard evidence for that - any demonstrative expansion of Zeiss would not have been popular and might have prompted the competition to protest against anti-trust law violations, so they'd have been discreet about it.
