Zbrush has a feature thats called UV master that is just brilliant at auto UV mapping. It will not work on a typical scan data mesh though. It need good topology so you have to do several steps to get the mesh up to scratch. All of that can be done with Zbrush. Sometimes a slow work flow though.
You could UV map automatically to AUV tiles in Zbrush but not sure if a UV like that has any advantages over the PS UV. Seems like PS is also using a similar approach to AUV tiles. In AUV tiles each polygon gets its own pace in the UV. If your mesh has 10 million polygons you can imagine the resulting UV mesh. Same thing with a PS generated mesh. Decimate it..
http://docs.pixologic.com/reference-guide/tool/polymesh/uv-map/Zbrush is a 800 USD software to.
The only reason to not use the PS UV is better use of texture space and editable textures. . Often i see only 20-40% of texture space used in PS generated UV´s. That means you will lose resolution. Also if you want to edit the texture or generate normal maps, spec maps etc a tiled mesh won't work well. If you just need the texture for renders it will most often be fine using the PS generated mesh and not worth the effort turning it in to a proper UV. Generate a 8k texture or even 16k texture and you will get plenty of resolution anyway. You can render using high ploys instead using a PBR render engine. A normal map will do very little effect on a high poly mesh. The best normal map after all is the real thing, a high poly mesh.
So try decimate the mesh to a mors manageable poly count and see if your texture improves.
I am not aware of any 3D app that can auto generate good UV´s from scan data with out modification .I high poly mesh is a nightmare to UV unwrap. If anyone does i would like to know as well.