On the USS Voyager, all senior staff report to the briefing room (plus local hitchhikers). I may be wrong, but it seems that the organizational structure of the ship doesn't include non-command departments like Stellar Cartography, Security MACO's or Counseling. But that all departments are headed by the likes of Chakotay (Command), Tuvok (Security), Engineering (Torres), Operations (Kim). Navigation (Seven and Paris) are the odd functions out.
They don't even seem to have enlisted Chief Petty Officers for transporters, etc.
So it may also seem that Janeway could have pursued a romance with Chaks (or Sevs) if she had really wanted. But it seemed like a personal decision not to - not an express regulation. They never mentioned it was Chak's belonging to the Command Department that would disqualify a relationship, nor that it would be different from anyone else. (Or it should have come up in Resolutions, I should think).
Still - Janes would put the ship ahead of her emotional needs. If she is to change the basic nature of her captain's role, best have a damn good reason for it. Her isolation was never a whim. She could barely bring herself to the holodeck, for that matter.
Early on, she told herself to be "larger than life" because that's what the crew would need to function smoothly long enough to make the journey.
A relationship with a senior officer may fly in the face of a lot of established character arc. Not saying it can't be done; am saying every inch of verisimilitude will have to be earned or it will come off as slashfic. Which is also fine, but distinctly different from "canon".
