Alright thanks for that Dylan What I've concluded, basically: Any ol' consumer m.2 drive is usable on the Poweredge r630 platform regardless of adapters or whatever shenanigans you throw at it. You should just not expect to be able to boot from such a setup, nor should you count on being able to use any sort of hardware raid. I got the machine to boot the OS on my internal NvMe drive by sticking a SAS HDD drive in there. I simply did manual partitioning during the Ubuntu install and placed my ESP/EFI partition along with a /boot partition on the SAS drive and the remainder (root "/" partition and SWAP) on the NVMe drive and all worked just fine. This setup is wonky as hell though and gives me zero redundancy. I was really just curious to see if I could see any major performance benefit by running the OS off an NVMe drive. I do not see - as of yet - any major benefit from doing this on this hardware. So what I've decided to do is get my hands on some sturdy SATA/SAS SSDs and stick a few those in my empty bays and use that for my OS and be done with it. The 4x NVMe drive bays I have with the NVMe enablement kit I'll use as my storage backend for linux containers, using ZFS (striped+mirrored). That seems to work nicely. However, I'm seeing very low performance numbers all things considered on my NVMe drives - I may just need to tweak some things and hone in on my fio commands, but on the surface of things it seems like the system in general is not able to utilize the full performance of my NVMe drives (I'm getting only about 50% rated IOPS/BW performance in most tests) - which may be due to the fundamental architecture of the system rather than the drives or my adapters. This is all "last generation" hardware, after all. I may update this post if I figure all this out at some point in the near term. In any case, thank you for your feedback here Dylan much appreciated. 
Poweredge R630 NvME M.2 Drive in PCIE Adapter in Riser 3 All Firmware and BIOS up to date as of today (March 18th 2020) --- I'm trying to install Ubuntu on my M.2 drive stuck in a Delock PCIE adapter. The drive shows up fine during the Ubuntu installation and after OS install it does show up in the Boot Settings menu but it is listed as "Unavailable: ubuntu" If I try to boot from it regardless, the boot fails. I have inspected the drive as I can chroot to it in the Ubuntu Recovery mode, and the first partition is indeed an ESP/EFI partition with the UEFI boot files in the correct locations. Why is my Poweredge unable to boot from this drive? What are the possible reasons for the BIOS listing it as "Unavailable" and what the heck does this mean? Any workarounds? I am going to try and install some other OS next and see if the issue persists ... I dunno FreeDOS or some other Linux distro or something if I can get that to work...
Unable to boot from PCIE NvMe device: What does "unavailable: OS Name" mean?