The latest version of P3dO pro (1.9.2) has a thumbnail generator. Manual or automatic (it's an option).
The thumb generation depends on the Poser preview render, which is not 100% accurate (far from it) but it's better than nothing.

The thumbs have to be made one by one. A batch thumb generator is under contruction and should be available in november/december.

Yarp
www.senosoft.com

Yarp - author of P3DO Organizer for Poser