(Last Updated: 2023 Dec 03 6:33 pm)
The Daz's millennium figures up to generation 4 can be used in Poser like you would use any other Poser figure. Daz's Genesis figures are not compatible out of the box. There used to be a script that allowed it, but that was discontinued. I think some people have had luck exporting as an FBX and importing into Poser, but I haven't looked into that.
As far as Poser figures into Daz, the older, non-weight-mapped ones worked with no problem. The weight-mapped ones aren't compatible, though I've heard some people have gotten them into Daz. You may want to ask in the Daz forum https://www.renderosity.com/forums/12452/dazstudio if your want to go in that direction. The weight-mapped Poser figures include Alyson 2 and Ryan 2, Miki 4, Roxy and Rex, Pauline and Paul, Pauline 2 a Paul 2, and Lafemme and L'homme. The poser versions of Dawn and Dusk are weight mapped, but there are Daz versions available.
IIRC, there's an excellent tutorial / sub-forum for getting Gen_3~~5 (V7~~9 etc) into Poser. Inspired by this, I ported 'Kalea V7 Rogue' to FBX, used it in P_11.3...
( Keep those head-ache pills handy !!)
Going the other way, you may be able to do it by simply exporting clad Poser figure as FBX.
Sadly, there seems no practicable way to use either DS' or Poser's 'dynamic' clothing facility to simply drape an imported 'nude' FBX...
For information, Willdial's tutorial allows you to use G3 and G8 with their morphs in Poser ;)
Here's a rendering of G3F in P12 Cycles
Poser 12, DazStudio 4.21, Blender 2.83 - LinuxMint 21 - Ryzen 5 RAM 16G, GTX 1650 VRAM 4G