Kaine's Pentastar Talks ability only captures true minor factions from the Minor Faction DLC, I.e. planets you can capture with an envoy. You can tell these planets are minors if you click on them and you can see they have minor faction abilities.
Special planets like Kuat, Coruscant, Mandalore are more like the pirate base. They are always hostile and cannot be peacefully acquired.
GoaFan77
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Project leader and creator of Star Wars: Interregnum and the Enhanced 4X mod.