Hydaelyn and Vana'diel are not the same world - they just share common features like simillar player races and some of the beast tribes (I've also heard people saying Hydaelyn is also FFIII's world, FFVI's world or even FFVII's Planet in different times, all of which is false).

The races of Hydaelyn are similar to Vana'diel's races, but they're not exactly the same (the XIV version of XI's galka for instance, the roegadyn, have females of their race, and lack the tails the galka have), so it just doesn't fit.

Yoshi is already aware of the popularity of viera, but he stated in the past he doesn't want to introduce that race to XIV because he would have to design a new male version of the race, and also feel that the 'animal/human hybrid' race is already taken by the miqo'te. So the 'one Steve limit' trope is very much in effect here I'm sorry to say.