The Samsung 950 PRO M.2 SSD is a NVMe drive, it is necessary to update the BIOS to version 0355 in order to be recognized by the NUC.
More details on the link below
BIOS v. 0355
Windows® 7 installation
After BIOS update, reset settings to default with F9. Then, disable xHCI mode at Devices>USB.
Plug Windows® 7 USB bootable drive and keep tapping F10, select UEFI - USB bootloader
Install the operating system
Then, you can enable the xHCI setting in the BIOS, it supports USB 3.0 devices.
Samsung 950 PRO M.2 SSD does not support RAID configurations.