Nope, they very much could have been added to towns! I honestly can't remember my reasoning for not adding them to towns, it's been a while. Maybe to make them more compatible with big mods that might tweak towns, or to facilitate killing them without antagonizing town guards. They were meant to be somewhat neutral and less centralized than the other groups, and so enjoy less protection!

Out of curiosity, is it necessary to add them as roaming uniques? Could they planted in a town or camp?

They do, it's Iyo in World's End

wheres the skitari leader located and do they have a base?