Have the famous (notorious?) DA DynaDrive crankset on 5
of my bikes and only 1 conventional DA crankset. The one you saw. Can't let this one go, as I would like to keep it for in case I want to switch to regular pedals on one - what I could imagine very well. Could help you with a DD pair though.
Ko Zieleman supplied only paying customers. The story goes that Ko was a quite an excentric person in general. Ko didn't like the idea of sponsoring. Everyone left his shop with a frame that was paid for. Doesn't mean there were no Zielemans in the peloton
Quite a lot 'brand x' racers with a Zieleman chassis underneath. Cause riding characteristics were simply 2nd to none for many sponsored riders. I do not know of a particular pro riding a Zieleman made frame, but that will be just my lack of knowledge. Would be happy to learn if somebody knows.