Umm you do know the Justicars aren't really the same side as the Republic right?
Not entirely true.
According to the Lore, The Justicars are made up of former Republic military personnel that were opposed to the Treaty of Coruscant. They are a breakaway Republic faction that is willing to use force against anyone who threatens their liberty. They are breakaway faction not essentially an enemy of the Republic. And of course they still hate the Empire.
Essentially I would envision a Justicars relationship with the Republic as being similar to the Smuggler. A independent group that shares similar goals with the Republic, but is not a part of the Republic itself.
Thats why I list it under "Republic".