Does the msi meg creation let you install the OS and boot up from an nvme pcie ssd?
Sure, you can install the OS on any NVMe SSDs installed on the motherboard.
If you're asking about the add-in board that is included (with the 4x NVMe raid), I haven't tried with that setup. Though even if it was not supported with the add-in card, you could likely work around that with a bootloader installed on a separate drive.
I had both, the "old" Gigabyte X399 AORUS Gaming 7 and now the MEG Creation. The latter is miles better than the Gigabyte board. Gigabyte isn't able to get X399 stable, BIOS support is non existant, bugs just don't get fixed, even if many people complain in the official forums. So if I need to decide again: MSI for sure.