I have had success with my own models, but I only went straight from Poser to Blender back to Poser. I was wondering why you are using UVMapper?
But anyways, if you are exporting entire Poser characters and welding seams, you are not going to get the same number of verts. Poser characters are made up of many smaller parts, and when you merge these parts, the joining verts are merged into one. Therefore, as soon as you export, you are destroying the original vert count.
Try it on a single body part, instead of whole character.
The whole reordering of the vertices will not prevent you from reloading in Poser, it just explodes your mesh when you morph. So if you are unable to re-import at all there may be somthing else going on.
Im not sure why you are rotating it on the X axis, I see nowhere in your post that you rotated it on the X axis to begin with, so there should be no rotation going on. (Unless you are rotating it in Blender and did not state this)
Here is the big one. When importing a Poser model into Blender, the models are scaled VERY tiny. When you do a remove doubles on it, because of its tiny size, the mesh will be destroyed! Even on a limit of .001, many verts are merged and deleted (especially mutated are the fingers and toes). You must first scale the model up, alot ... , before you rem doubles. Of course then you have messed up your perfect target, so I suggest scaling by a specific number, so you can scale back down the exact amount before exporting.
First, I suggest not using UVMapper or anything else (wtf is a "Compose" ?) Export from Poser, and then import it directly back into Poser as a morph target. If this is successful, then you know your on the right track. Next import this file into Blender and directly export back out, with no changes, at all. If THIS file imports as a morph target, then you are still on the right track and are ready to proceed.
If all fails, go back to a cube! Surely Poser can get a cube right?