I have never seen one of these either, but I guess it's possible. The parts catalogs show that there were two hex L-arms available (one long and one short), but they were not cymbal holders. They were accessory arms. Pic below is from catalog, and the other pic is the short L-arm I have mounted on a bass.
[Attachment: 75109] [Attachment: 75110]
All the cymbal L-arms in the catalogs are round rods which enabled them to rotate in the Knobbies. The round L-arms ended with a hex tip at the base of the threaded cymbal post which allowed a Swivo tilter to be attached. I wish the seller showed a pic of the cymbal post with the washers removed to see if this is indeed a legitimate Rogers part. Perhaps this hex cymbal L-rod could have been designed for a cocktail kit or a Cozy Cole setup which had a million different possible configurations.
Any other guesses? Ploughman, GaryN, DanC, Dan B.?
Mike