I was working on 970 EVO Plus with Sonnet 4x4 pcie card these days.
Finally it works, for several hours and restarts, including Mojave installation.
In Samsung Support site, there is an ISO file of firmware update utility for EVO Plus, named
NVMe SSD-970 EVO Plus Firmware
Download various software related to your product, including Samsung Magician, designed for use with Samsung's memory products, and find related information.
www.samsung.com
Also a User Manual for downloading:
Follow this manual to download a UNetbootin freeware, and step by step to create an EFI Boot USB.
unetbootin.github.io
Download the Unetbootin for Mac and open it, ignore the alert that it may not be compatible
It can create an EFI bootable USB working with Mac.
Startup with the boot USB, step by step, it will update firmware to drives one by one, even in a RAID set.
For the system installation, I formatted the drive to APFS, and it ran very smoothly.
My System: Mac Pro 2010, 12 cores, 5,1 of boot ROM 141.0.0.0.0
OS: Mojave 10.14.5 (18F132)
PCIe card: Sonnet M.2 4x4 PCIe card, x16 PCIe 3.0, up to 4 SSD's