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The tat's my thoughts on it- the SITH TATs are the RED, Mauls Dathomiri tats would be the black
Other Sith (Legacy era) would mimic Maul's styling.
No the Witches of Dathomir will cause Palpatine to grow fearful- thus cutting the planet off. The Chun'thor had already crashed there some time ago and Yoda himself had to negotiate the Jedi survivors release. At some point Palpatine will as Emperor declare the world a quarantine, in a sense. Not allowing any ships onto the surface.
The Iridonian's men- The Nightbrothers are warriors they were training to be that, Dathomir is a barbarian type of place in many ways at the point. Their culture (Nightsisters, Witches, and now Nightbrothers) was what drove them.
The women prized strong men, but they had a very definite hold on the males. They were slaves in a sense- if not out right.