try exporting without groups in export settings.

export the figure with all export settings unchecked, reimport with just weld identical vertices. the figure is now one piece (a prop) with all material regions intact and no splits at the groups. works with Gen3, Gen4, whatever.

edit_ haven't used the latest version of Poser so maybe the is a curve-ball that I'm unfamiliar with, usually disabling groups on export and then welding does the trick though.