I have a similar problem with one item. It is a hair file called “Amarseda A3.daz”. When loaded, it shows up in the Scene tab, but not in the viewport. If I hover the cursor over the viewport where the hair should be, I see the hair highlight in orange, just like any visible element does when the cursor hovers over it. However, If I select the hair in the scene tab, and look at the Surfaces tab, everything looks OK - diffuse, opacity, etc. If I apply another material preset, still nothing shows in the viewport. If I load an old 4.0 DAZ scene that used the hair, the hair shows up just fine in the viewport. I think something must have changed in DS 4.5 to make the old DAZ file incompatible. I remember Ken (SBRM creator) saying he changed file formats in his products, because DS at some version would no longer load old DAZ format files.
Edit 9/10/2012: I installed the Poser version of Amarseda hair to see if it works, since the DS version does not work. The Poser CR2 file works fine, but the DAZ file still does not work in DS 4.5 Pro.