Well Maul is an ideal example, not saying Kenobi's Jar Kai has gone as noticed, but it remains a valid example.
No, I don't think the creators of TCW were thinking Kenobi is a Jar Kai and Niman master, just as Lucas/Gillard probably were not thinking Maul is a Juyo and Teras Kasi master at the time of TPM.
Nevertheless that is exactly what they have shown us. At the time of TPM, they were probably thinking this guy is going to be very agile, acrobatic and the s*** with a Lightsaber and Saber Staff. Whilst the creators of TCW were clearly thinking, Kenobi is a very skilled swordsman and can wield dual Sabers exceptionally well.
TFUII states Ataru and Niman are the basis for Jar Kai mastery. Given all the acrobatics Kenobi did in the Maul/Opress fight, it seems he's kept himself very competent in his Ataru skills. Then given how he combined them with some exceptional Jar Kai, it's really not a stretch at all to assume he's very competent in Niman too.
Of course saying he has Niman mastery can not be stated as fact until it's stated somewhere, but given the evidence it would seem to be true. But it doesn't really matter. What matters is Kenobi is obviously very good at offensive as well as defensive, and that he is trained in different styles.
Originally posted by Nephthys
Not sure why Jar'kai also gives you Niman by extension. In The Jedi Path Anakin notes that he's been studying Jar'kai with no mention of Niman itself.
It's what Hansel was proposing, but I believe it might be stated in a few sources that a requirement for studying Jar Kai is mastery of Niman.