all you need is the Mojave patch app and a thumb drive...
get the patcher here:
http://dosdude1.com/mojave/
Leave your OWC AURA in the MP6.1
download the full-size Mojave installer with the patcher app (tools > Download MacOs Mojave)
and create a modified installer for unsupported Macs (even so the MacPro6.1 lists as supported) unto your thumb drive
restart from it and install Mojave to your now miraculously supported internal AURA
(be patient it needs quite some time without showing you any progress, go jogg in the woods or watch am movie...)
Worked for me with a 4TB OWC AURA SSD in a MacPro6.1
and upgraded my previous HighSierra to Mojave, didn't need to reformat the drive and migrate my data from backup!