How could they even be in uniforms when they are not Starfleet? I would imagine Starfleet is pretty precious about who gets to wear the uniforms. If you were going to stick 7 in a Starfleet uniform you might as well have stuck Neelix in one. If you were going to stick T'Pol in a Starfleet uniform you might as well have stuck Phlox in one.
Interesting of course that neither Phlox nor Neelix wore catsuits.
I think of Seven of Nine as Starfleet - at least as 'Starfleet' as many of the Maquis. She was certainly a serving part of the crew, and not - as with T'Pol - seconded from an allied fleet.
As for Neelix, sure: put him in one too. He can have Harry's uniform after he's thrown out of an airlock.