Before I go and buy that motherboard; I want, if possible, your
confirmation about that.
Yes; The Intel Xeon E5-2670 v3 is compatible with the MSI X99A SLI Plus
Intel Xeon E5-2670 v3 Specifications:
MSI X99A SLI Plus Specifications:
Although the CPU in question is supported by the intial firmware for that motherboard ( 1.0 ). You should still update the firmware to the current revision. I determined that the intial firmware of the motherboard supports this CPU, by the fact the CPU compatability table references 7885v10.zip, as the revision that added the support.
If you recieve a motherboard with that revision (or any revision except the current revision) of the firmware for that motherboard you want upgrade to the current version for system stability and memory compatibility reasons.
The specific motherboard you asked about has been on the market for nearly 3 years. We cannot predict which revision of the firmware the motherboard you will recieve.