In my dojo, we do something similar. When testing for 1st kyu, the student is required to demonstrate at least three different defenses against a tanto attack (Shomenuchi, Yokomenuchi, and Munetsuki attacks -three different techniques against each attack). Often, a static attack such as a grab while holding the tanto to the nage's back or side is also required. The test is usually performed using a wooden tanto, but occasionally a real blade will be used, at least one with a sharp point.
When testing for Shodan, the student is required to demonstrate three different defenses against each type of attack (Shomenuchi, Yokomenuchi, and Munetsuki) with a bokken (Bokken Dori). I've never seen a Shodan test where an actual katana was used. I can see the benefit though. It would certainly make the nage more aware of the weapons blade edge. Too often I've seen nage who forget that the bokken should be treated as an actual katana and that it does have an edge (although not a sharp one). Hope I've helped you out.