Of course, we don't really have a reason to believe that there would be
any humanoid species called the Trill.
Judging solely by the episodes, it's the slugs that are called Trill by species name; everybody else is merely a citizen of planet Trill. And they have always been capable of living in more than one kind of humanoid body: in "The Host", both a ridgeheaded species and
Homo sapiens were found compatible.
For all we know, neither of those was ideal for the slugs, though. They would have chosen the optimal host type through experimentation, and most would have ended up using Kriosians, the species that Dax apparently is a member of (just go see "The Perfect Mate" and "Precious Cargo" for confirmation)...
I know that in "Eqilibrium", it's claimed that only a select few members of the one and only (Kriosian-looking) host type are compatible with the slugs. But at the conclusion of that episode, this is revealed to be a big fat lie. So there's no inconsistency there, and no limitation on the type of humanoid face that a Trill can take. For all we know, there are a few Klingon Trills and Pakled Trills out there, too.
..it doesn't seem uncommon for Trills to serve in Starfleet. Is Trill a member of the Federation?
There are Klingons, Ferengi and Bajorans in Starfleet, too. Doesn't mean Klingons, Ferengi or Bajorans would be members of the Federation.
And Kurzon Dax was a respected negotiator mediating the UFP-Klingon crisis. Sounds like he was a neutral character, hence probably not a UFP citizen at all. Perhaps Trill was a member but Curzon has expatriated himself; more probably, Trill wasn't a member, and never became one during the course of the various Trek series.
Terry Farrel who played the first Dax looked ugly with the TNG Trill makeup
From what I've read, she also got a bad allergic reaction from the full makeup, and had to be given the most superficial paint job only. Of course, always the masochist, Westmore turned that "superficial" job into a painstaking application of complex art, which he signed after each application... The story doesn't tell where the signature went.
Interestingly, since each application was unique, we're apparently to believe that the spots on the spotted Trill hosts move around. But that was always true of the Kriosians...
Timo Saloniemi