Is the SM951 AHCi drive the only drive you're using?
If so, than you can't install the RST driver because the SM951 is connected to the M.2 PCIe connector which has its own AHCI protocol, which the RST driver doesn't support. If you install a drive to the normal sata port than you're be able to install the RST driver.
And yes, the Windows driver is just fine, it performs very well. That was my experience when I had the SM951 AHCI drive in my NUC5i7RYH.
In this case, if you’re not doing a raid configuration in your system there is no need to install the Intel® Rapid Storage Technology. You can also have it installed when you install the operating system in AHCI mode but if it you can’t install it, that is not going to do anything wrong in your system.
I’m glad to hear that you Intel® NUC is working fine.
I would recommend checking with Samsung the bench you made with Samsung SM951 to check if that is the correct result.