Fate at least tries to expand on Nobukatsu in that he intentionally failed his coup against Nobu both times, it was explained Nobu faced a lot of opposition from traditionalist elders as they wouldn't accept a woman leader, his coup attempts were deliberate attempts to root out said elders and give Nobu the opportunity to get rid of them without being questioned, and he kept his plans secret from her as to make it impossible for anyone accuse her of plotting with him, he wanted all her reactions to be genuine, and he loved his sister so much he was perfectly willing to sacrifice his life for her.

Fate alternate history means they can expand on any historical figure if they really want to, and going out on a limb to say that the heroic nature of Nobukatsu's sacrifice just barely qualifies him for a Heroic Spirit would be enough for most people, plus, the Fate version of Nobukatsu character certainly seem popular enough to get a welfare position if a third GudaGuda happens plus even I agree we need more male welfares.