I'm not so sure you can do this in UV mapper, but I gather Kalypso has done it- what Poser expects is that the groups have duplicates of the vertices at the joint, one for group. Poser is also very, very fussy about anything in the IK chain, you run into all kinds of the problems when what you are doing breaks it's (undocumented) rules. However, the rest of the parts should still show up, and Poser will let you know if you did any of the obvious things, like have the obj name in the wrong case.