I have a 1957 Walter Röll in 5,6x61 SE vom Hofe. As you say, Röll's name is stamped on the under barrel and hidden by the stock, the floor-plate is aluminium & the trigger guard stove-enamelled. Stock has fine oak leaves and action is silver and scrolled.

There's nothing by way of a name to suggest it was handled by any other gunmaker and the proof marks are all German (Ulm proof-house). However the previous German owner was adamant that he'd purchased it off Karl Hauptmann of Ferlach. Rifles made by Hauptmann in this era all start with a serial number 23 XXXX and this rifle doesn't, so Hauptmann dismissed my suggestion it may have been once associated with them. However, as you say, perhaps a customer simply wanted a more basic rifle than they made in Ferlach and they were happy, in this post-war re-establishment phase, to supply it without their mark. It sounds like Röll happy enough to supply other makers.