AFAIK the only difference between male and female dwarves are the 'he' and 'she' tags. If you took those out in descriptions of 10 seperate dwarves you wouldn't be able to tell which where male or female.
Dwarves don't have transgender because it isn't an issue, because both sexes are in no way biologically different. Toady has not introduced their method of reproduction into the game, and the lore is definitely not clear on this bit. If anything the words he/she wife/husband are lost in translation from the dwarven language, and simply mean that there is one dwarf that carries the baby into battle, and another dwarf that watches that dwarfs back.
This is not to say that I am against modding transgender into the game, however I wouldn't personally use said mod.
"Urist feels privileged for being a male, pale of skin, heterosexual dwarf."