IME, Poser 5/6 support at DAZ is spotty. DAZ does actually sell some P5-and-above only products now, such as dynamic dresses and Tiny's dynamic fur for the MilCat. (Never thought I'd see the day!) Some of their products have P5/6-friendly MAT files/textures, some don't. This is easy to fix, but it's tedious. Particularly annoying are their construction-type sets (the castles and such). The product consists of a bunch of separate props, which makes it a real pain to fix all the bump maps.

Some of the older DAZ products don't work well with Poser 5/6, simply because they were made before Poser 5 came out. There are some that you have to turn smooth polys off to render, and at least one that has the "L-shaped polygons" problem. You can find these problems with older products in any store, though, and usually if you render using the P4 renderer, they're fine.

I have had some problems that are not easily fixed. Notably with hair. Noisy textures, backwards-facing polys, that sort of thing. (The Wedge Hair 2 does not work well in P5/6.) But these are few and far between. And they do have that 30-day money-back guarantee, so if the product looks bad in P6, you can always return it.