Area 51, compatibility of Samsung 970 Pro

There is not an M.2 slot on the motherboard. You would need a PCIe adapter and then I don't think that the most recent BIOS supports booting from an NVME drive. You could of course install a 2.5" SSD. But the speeds are much slower than NVME. I assume, by the way, that this is a straight Area 51 and not an area 51 R2, R3, etc.

I'd be shocked if you have any compatibility issues since I believe you have the R4 or R5 version of Alienware Area-51, which has a M.2 NVMe SSD slot and was sold with NVMe SSDs.

The original Alienware Area-51 (and likely some follow-up versions) would need a M.2 NVMe to PCIe adapter as JOcean mentioned.  Any M.2 NVMe SSD should be usable as a data drive even in the original version.  The Samsung 970 PRO and most M.2 NVMe SSDs would not boot, though.  But, the earlier Samsung 950 PRO should, since it has a Legacy BIOS Option ROM.  To boot on the original Area-51, the Samsung 950 PRO would need to be formatted MBR and not GPT, since the machine doesn't have UEFI.  Note if the machine's PCIe slots are PCIe 2.0 rather than 3.0, you'll get half speed - so instead of being capable of around 3500 MB/s you'd top out around 1700 MB/s.  Still, not bad.

Will a PCIe NVMe - M.2 Internal SSD work on the Area 51 R2 with the I7 6950X X99  Chipset? I need faster speed than the 2.5 SSD can deliver. Thanks again

Yes, a NVMe M.2 SSD has been shown to work and is bootable with the Alienware Area 51 R2 - Samsung 950 Pro and 960 Pro.  See thread here.  Any NVMe M.2 SSD should work.

...seems on Area 51 R2 the PCIe x4 slot is PCIe 2.0, so if you want PCIe 3.0 speeds you'll need to put the NVMe M.2 to PCIe adapter in a x16 (or maybe x8) slot.  See post here.