i don't use it for zoning unless i find i have a model that needs its normals to be corrected, and for actual grouping a rig, but Poser has a way to create material zones via the Grouping Tool...

what i actually use, because it's super easy and cheap, is the free version of Hexagon you can find over in the Daz store...

when you import an OBJ into Hex, you'll be able to see the zones that have already been assigned.  you can then further assign zones as you'll essentially be seeing the model in its wireframe mode, allowing you to precisely select whatever polygon[s] you see fit.  

it'll take a bit of time, but i can create a few screenshots and such to show you what tool to select, etc., though Hex has relatively easy-to-understand documentation.  i mean, if i can figure it out, i'm pretty sure my cat could if she read English at all... heh...

there are other tools i use in Hex, most likely improperly, because of faffing about & experimenting and finding what works for me/my needs/wants, and my habits are most likely questionable, and would not be recommended by any professional modeler, but hey, i'm just doing things solely for my own use and honestly don't really care about "proper"...

and again, i will reiterate, that since i am zoning what are polygons, there are limitations because there might be ways that a mesh has been constructed that is not as conducive to zoning as other meshes might be [and i should say that it is this that started some funky thinking in my head and probably bad workarounds because i didn't want to take "no" for a full flat out answer]. basically, you're somewhat enslaved to the design of the mesh...