At the moment, both companies have to play well together.  Poser has the largest and longest established user base (meaning most of the money spent on content will go to Poser content). DAZ has the largest content store for Poser.

Occasionally there are interesting bits of cooperation.  About half a year ago, I saw a vendor at DAZ selling a Miki outfit that was not offered with a version that was compatible with a DAZ figure.

My visual indexes of Poser content are at http://www.sharecg.com/pf/rgagnon