You can transfer texture from a hi res to a low res mesh in Topogun, even a poly painted mesh from ZBrush -you do need to UVMap the low res mesh though. So after you retopo, you export out to OBJ, UVMap, then reimport to Topogun. As for topology of the mesh - you have total control of that. You can add or remove topology in Topogun however you want. So there's nothing stopping you from placing edges where you think seams will be. The demonstration idea was purely about how long it would take to do it, not so much about the topology itself.

 

Also, when doing retopology work for public consumption, I find it's easier to set up material zones AFTER I UVMap the newly made low res mesh. The way I do it, my UV islands are always exactly the same as my material zones (with the exception of eye sockets). This makes it a simple thing to select and assign material zones.

When retopologizing a textured ZBrush mesh for personal use, I don't bother with material zones, as it's usually the texture that's important to my need more than zones themselves. I may go in and assign the eyes or teeth their own zone but that's about it.