I've seen lots of exos in the tower with serving jobs like being a post person, cleaning, or being a guide. I feel like this is the proper role for all exos as I don't think they are very adept in combat. Whenever I see exos in the crucible I feel like I should destroy their ghost as well so I can dismantle the exo and use their parts to upgrade my weapons.
If you look at the Grimoire card for Exos, it clearly states that the Exo race was built either by humanity, the Traveler, or some other force to fight in some type of war. Also, the robots seen at the Tower (cleaning bots, working at the bounty station or as the postmaster) are not Exos, as all Exos are designed to look visually similar to humans.