Pretty much all Poser props can be used in DAZ, at least in the 3DLight renderer, it's a little more work using them in IRay. I generally will leave reviews specifying compatibility with DAZ because if an item can be used in both programs, it increases the available pool of potential buyers, and vendors here are going to make what sells.

Can't help you with the Human Figures, there is just too much going for the Genesis family to use any figures for Poser.

As far as any "debt" DAZ has towards Poser... Um. So what exactly do you expect a competing company to do for history?

Use whatever program you want, but unless vendors like to work for free, expect them to make content with the widest possible appeal.