What version of Poser are you using?

You can group the model in Poser using the grouping tool. You won't lose your UVs that way. Don't break the model up, just create the groups you need by selecting the polys for each group with the grouping tool. Afterwards, delete the main object group (whatever the name of your model is will be that group). If you're using P10 or PP2014 the grouping tool is much easier to work with and you can mirror your groups across the X axis. 

I'm not familiar with using hexagon, but any program you use, just export the whole model after you've mapped it, and bring it into Poser.