Yea the original export used the sketchfab preset and resulted with that same error. The issue according to Allegorithmic support dude is that their 5_5 shader is bugged and using 'pbr-metal-rough' would work just as well.
All in all it's just something to look out for. I'm still cleaning up my pbr workflow and breaking some bad habits. Initially I wasn't sure if this was all due to some gap in my training.
I got a reasonable result by inverting the main values prior to export but it was a bit tedious as it takes some time to process any changes. The inverted skin glossiness/roughness turned out nicer so I ended up toning it down in SP2 while boosting the mangey scar tissue. That's a happy accident I guess.
@lord00120 Yea I think he should be holding something thuggish.