I've done that before, working on a lower resolution mesh and then importing onto a higher resolution mesh. It's especially useful for expression morphs as it's easier to grab loops and chunks of topology for area changes that predictably effect neighboring areas.

If I remember correctly I would sculpt on a lower res mesh, load as morph, export again, subdivide, and load that onto a higher res version in scene. So I was working on a couple of obj/prop versions of the figure in the same scene, each at a different resolution. I think the extra step was to maintain vertex order as I was using wings and it's magnet falloffs to do the morphing and subdividing. Blender and it's proportional editing feature has replaced wing's magnet options for that kind of stuff for me. Basically the same though, but with more conventional gizmos and adjustable falloff cursor. Back then I was using Poser 8, I jumped from using version 8 to 11.

Anyway, subdivision morphs have a couple of different ways of working in Poser... Depending if you bake down for subdivision. Its basically "works at any res or works at a specific level". It's in scene subdivision, via unimesh skinning, rather than rendertime micropolygonal displacement.

See chapter 36, page 940 of the user manual for using subdivision morphs in Poser with the morphing tool. Also there's subdivision support and a bake down option with GoZ to Zbrush. I suspect that you might be able to use sculpting tools other than the morphing brush or Zbrush for subdivision level morphs in Poser (such as blender, mudbox, or even wings) but it requires an export method that maintains vertex order after welding and a means to produce a viable obj with poser subdivision on export. Exporting directly from poser to obj with poser subdivision active produces an empty obj file. Using a utility like PML maintains a viable subdivided obj via the exporter but I haven't fully tested the results.