First of all not all WWI propellers looked the same. To get some idea of the variety have a look at the following page:

http://www.woodenpropeller.com/Photo_Gallery.html

So the question becomes what does the propeller on YOUR PARTICULAR aircraft look like? The earlier aircraft tended to use the stereotypical "scimitar" shaped blades with high pitch (to compensate for the lower powered engines) while later aircraft like the Fokker DVII used a fairly "modern" looking prop.

Additionally while virtually all WWI props were laminated the laminations were rarely as visible as the scale model props commonly seen with their exaggerated brown and white striping. For my Fokker EIII I looked into the scale prop question extensively but in the end couldn't locate a scale prop in the 13" size I needed that looked significantly more scale than a plain old wooden Zinger.

My solution? Strip the varnish on the Zinger, stain with Mahogany, and relaquer. It may not be scale but a truly scale prop probably wouldn't have be right for the model engine.