After my earlier posts on this thread, I attempted to hack the NVMe vs. SATA logic present in DSM and was not successful.  The device configuration is set up by a completely customized udev which deliberately separates NVMe from SATA, and all their tools and utilities work quite hard to enforce this.   Similar to the reddit poster, I was able to manually create arrays with NVMe members, but any change to the array using Syno tools (as I recall, even a resync) caused it to break.