Most likely not. Usually, such works are the product of the author's imagination and creativity rather than being based on actual happenings. 'Pulang' seems to fall into this category.
I'm not sure who Aku specifically is. Aku could be a person with a great imagination who tells all kinds of stories, like adventure stories, fairy tales or even true - life stories.
The main plot of Niu Pulang was that he pretended to be the late poet Niu Buyi and became a famous poet by impersonating him. Niu Pulang had obtained Niu Buyi's poetry collection by chance. Because they shared the same surname, he decided to impersonate Niu Buyi. He made friends with the powerful and befriended Niu Yupu, and successfully sent the big swindler Niu Yupu away. However, the real Niu Buyi's good friend, Feng Zhuo 'an, exposed his true identity, and Niu Pulang was reported by Grandma Niu. However, the foolish Xiang Zhixian let Niu Pulang off, allowing him to continue to impersonate Niu Buyi. Niu Pulang's story revealed the dangers of human greed and vanity, as well as the existence of deception in society.
As I don't know the details of the 'pulang real story', I can't determine its significance. It could be significant to a particular group of people who are related to it in some way.
I'm not sure specifically what the 'pulang full story' is as it could be a very specific or personal story. It might be a story related to a particular place, person, or event named Pulang.
It seems that Pulang Araw isn't based on a true story. It's likely a concoction of the author's imagination and story-telling skills to engage the audience.
It could be someone from the Naruto universe who doesn't like Naruto's newfound fascination with Aku. For example, Danzo might see Naruto's interest in Aku as a threat to the stability of the village and try to stop Naruto from further exploring Aku - related things. So, Danzo could be the main antagonist in this case.
The character of Aku could be developed in a 'pregnant Aku in Samurai Jack fanfiction' by exploring how he interacts with the world around him differently. He may become more reclusive as he doesn't want others to see his 'weak' state. Or he could become more aggressive in trying to protect his pregnancy, which would be a new aspect of his character. Also, his relationship with his own power might change. Maybe he has to find new ways to use his magic that don't harm the unborn, which would force him to grow and adapt in ways he hasn't before.
One idea could be a crossover where Aku accidentally opens a portal to the Naruto universe. Naruto, being the curious and brave ninja he is, decides to explore Aku's world. They could start off as enemies, but gradually come to understand each other's motives and end up teaming up against a greater evil that threatens both of their worlds.