It would make sense, sort of, even if he were a biological humanoid CMO. After all, his rank would be rather meaningless when dealing with non-medical issues, and he would have no medical staff to pull rank with. And whether his rank affected his pay or not is pretty moot in the context of VOY if not in the general context of 24th century Trek already.
IIRC Torres was supposed to be a Lt. JG, Paris a Lt. The reason why I said this is because (i forgot the episode name), during a warp core breach, Torres orders everyone out of engineering, but Paris says "you can't order me, I outrank you".
I think this was in "Day of Honor", where both characters already wore the pins of Lt(jg). But Paris would theoretically outrank Torres in any case, in the sense that Paris got his commission in "Caretaker", while Torres got hers in "Parallax", several days later. And the officer with more days on a rank is senior in the relevant sense of the word: he gets to order those people of his rank who have spent fewer days at it.
In fact, VOY's first season introduced a never before seen rank, Crewman First Class, as seen on several of the Marquis crewmen in Learning Curve & Seska.
Crewman 1st Class was first mentioned out loud in TNG "Drumhead". Supposedly there are at least two, possibly three or four different rates of Crewman, like in the real world, even though none have special insignia in the TNG era.
The insignia on those VOY personnel were identical to the thing that Torres wears on her collar: everybody in the Maquis save for Chakotay (and Torres in some early episodes) was wearing the Lt(jg) pin, and we weren't supposed to notice. Indeed, those pins were so hard to read that it's easy to pretend some weren't Lt(jg) but were instead Ensign (as Seska should have worn) or perhaps Crewman (a never-before-seen pin in modern Starfleet, to be sure - previous 24th century personnel only wore rank markings if they were commissioned officers, some O'Brien haziness notwithstanding).
The confusing part is of course the costume screw up, where Tuvok was wearing a Lt. Cdr. rank, Torres a Lt. Attempts have been made to explain this, and include the fact that both Tuvok & Torres were demoted off screen for the events where they defied Janeway's orders and gave Voyager's library in exchange for transporter technology (again I forgot the name of the episode).
That'd be "Prime Factors". The demotions would come by the time of "Cathexis" a couple of episodes later, and would be a rather logical development - but "Cathexis" itself isn't logical, because Tuvok's rank pips fluctuate from scene to scene there.
Timo Saloniemi