I've thought that it would be interesting to have a Human officer wearing a hijab on duty. As long as it did not interfere with the wearers vision, hearing or ability to speak. Depicting a Starfleet that is conscious of cultural diversity.
Riker problem with Ro wasn't (imho) her ear piece, it was Ro herself, Riker didn't want a convict aboard the ship where he was first officer.
In the episode where Riker apparently) lost his memory, there was a female Ferengi coming out of a turbo-lift, who was wearing the the Ferengi headcloth with her uniform.
The impression I received is that Chakotay wasn't required to remove his tattoo during his time in Starfleet, and then had it re-applied.