Runevn,   The card is compatible, it likely wasn't added till after the guide was released. I would make sure the server is up to date completely prior to installing it. The page you provided the link to verifies compatibility at the bottom of the page.    As far as the differences, the Base T is copper where the other 2 are fiber, and the differences between them is manufacturer.   Hope this helps.
I have a Dell r720xd with a Broadcom 57800 SFP+ (network daughter card) installed but I experience compability issues with my DAC cables, thus I have been looking at replacing my Boradcom card with this Intel X520 Dual Port 10Gigabit DA/SFP+ (network daughter card) (Dell part numer: 540-BBHJ). However, in the technical guide for my Dell r720xd this card is not in the list. Does this mean that this card is not 100% compatible? In the Technical guide the only Intel card that is listed is the Intel X540 Base-T card. Furthermore, what is the main difference between: X520 SFP+ NDC, X540 Base-T NDC, and my current Broadcom 57800 SFP+ NDC? Thanks in advance.
Network Daughter Card for Dell r720xd