What version of ZBrush are you using? I found out the hard way that for some reason most of the tutorials made the process way more difficult than it needs to be. I use Zbrush 2 (I know, how archaic.) my process is-

Load figure in poser

0 Figure

export wavefont object, single frame.

Click universe to unselect all elements in the poser scene.

Select desired body parts , and perhaps adjoining to avoid distortions if you edit too close to seams.

Tick only include body part names, include existing groups in the dialog.

Export as wavefront object

Open ZBrush

Go to Tool pulldown menu, click Import

browse to .obj, Import

Tool will load, Drag onto canvas

Click Edit (and frame if you want to see the geometries edges and groups, makes it alot easier). Each group will be assigned a different color.

DO NOT move the Tool in cartesian space, only brush and edit the topology. Although you CAN use the move brush as this is just editing the topology.

Finish your editing.

Go to Tool pulldown once again, scroll to bottom (NOT the top export option) to export. tick only Obj, Grp, Qud and scale setting should be set at 1. click export. do this for each individual edited body part separately or the multiple body parts will all export as one object and won't be usable as morph targets. you can selectively hide and unhide the various body parts on the canvas of Zbrush by clicking control+shift in the canvas area or the object parts. If a body part is hidden on the canvas it will not export.

Load as morph target on zeroed figure in poser.

While in Zbrush you might want to save that edit as a Ztool so you can do some more editing more readily. I usually have Wings3D, Poser, and ZBrush open simultaneously as my workflow.

Again, this is for Zbrush 2. Never once had to use any scaling utilities with this workflow, despite all kinds of tutorials saying that I would. Who knows? This method has worked perfectly for me for years now.