Hi cwmanley,
I recently purchased Skinn pro to transfer blendshapes from one model to another inside of unity. I tested the models inside of Maya and the transfer worked as expected so I know its not a matter of the vertex order being different. I used all of your recomended import settings and unfortunately the best I could accomplish after a few hours of tweak was some really funky results using the vertex mapper game object. The copy and past blend shapes never worked between models. I was able to apply blend shapes to the exact model with the copy and past function but not to a similar sized model with identical vertex order. (but overall different shape) I saw the youtuber "Cutscene Artist" do just this in her video "Skinn Pro: Extract load transfer blend shapes in Unity." So far I have tested this in Unity 2019.3.9 and 2019.4.9 I'm going to keep working at this but if you have any idea's what could be causing my problems. I would love to know! Thank you so much!