In a manner of speaking, yes. When you import a completely welded (aka "unimesh") OBJ into Poser and then convert it into a figure, Poser splits the mesh apart at the group boundaries. If you export that OBJ back OUT from Poser, you have one of two options. If you don't weld the mesh each of the body parts will become a separate OBJ, and trying to morph it in a third party program will be difficult because the group seams aren't welded and they will become separated. 

But let's say you tell Poser to weld the OBJ during export. It welds the OBJ together at the group boundaries, but for some odd reason leaves one set of the vertices still inside the OBJ, floating and connected to nothing. If you try to bring this OBJ into your sculpting software, each app handles these floating vertices differently. Some allow you to weld the vertices together by choice, others do it automatically. No matter which way, the end result is the same .... the vertex order of the OBJ file changes, and when you dial the resulting morph in Poser, it "explodes" and doesn't work as expected.

Geting the vertex order back so the morph works properly isn't always easy. Some apps have ways to fix it, others don't.  Where this becomes most problematic is, if you do a "copy morphs from" to copy morphs into clothing, and then want to export one of the morphs to clean it up in your modeling software. It ends up being three times more work than it needs to be. 

Back when Poser was first written, it broke the mesh into individual groups to make it easier on system resources. Now that computers are more powerful, Poser can be updated to work on the mesh as a whole. But there are years of code to dig through and update to make it happen. And as someone has already stated, the fixes go deep and touch almost every aspect of Poser.

As far as the FireFly vs SuperFly thing, I far prefer SuperFly because it has PBR (physically based rendering) capabilities. You can use something like Substance Painter or an equivalent to create PBR maps with metal-rough workflow. All of the magic is done with texture maps (usually a minimum of diffuse, normal, and roughness, but also transparencies, metallic, emission, and others). No fancy node tricks ... and the maps you create work equally well in Poser SuperFly as they do in Daz Studio IRay.

So really, associating the "Unimesh support" with "better Genesis support" doesn't touch the heart of the issue. "Genesis" is more than just a unimesh, it also deals with other features that work in conjunction (auto fit, auto smooth, etc etc etc)