Cool technique!
Cindi, I believe that PTI Impression Plates do leave a debossed design. (They press the design into the paper). When I went back to the challenge website and looked at the submitted cards, I noticed that some people did use the embossed side created by embossing folders. They were fine, but the stamped images covered the embossed lines as well as the background so the stamped image was complete, not interrupted by the debossed design. I hope that makes sense!
Please feel to correct me if I'm wrong about those plates. I've never had one, but I've been drooling over the Linen Texture/Canvas one (temporarily out of stock forever)
Daria
ETA: On some geometric patterns, it would not matter since the embossed and debossed areas are pretty much equal--think stripes and chevrons.