does chamberlain of the six samurai count as a six samurai monster?

Yes, since his name does contain "Six Samurai."

More than likely, we will have MORE Monsters that have Six Samurai in their Name, but they just wont be the Original Six Samurai, like Zanji and Grandmaster, but as long as Six Samurai is somewhere in the name, they will be considered legal to use for any effect that calls for a Six Samurai.

technically, the original Six Samurai are Zanji, Irou, Yaichi, Kamon, Nisashi, and Yariza. Grandmaster was thrown in take actually make the deck playable.

The point was, they all came out together for the English Meta. There might have only been 6 in Japan, but we got Grandmaster with the release of STON, so there was no, "And soon you will have Grandmaster...."