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.
As stated by other people, the individuals you are referring to are likely robots who are [i]not[/i] Exos. Moreover, Exos are sentient, individual beings, therefore putting them in any sort of set "role" or "box" or making societal generalizations about them is morally wrong.