The most common use of the word "server" in the US is in connection with a critical piece of computer equipment. It is also used by a certain class of restaurants (the kind that have pretensions of five-star grandeur, where the wine cellar is two or three times the size of the dining room and there are no menus because the wait staff recite the day's offerings from memory without mentioning the exorbitant prices) but most Americans don't eat there. We go to the cozy, little neighborhood spot where we know everyone by name.
It might be the most common meaning for people who are involved in information technology (and even then the purely software meaning of “server” might be more common than the hardware meaning, which runs such software), but for the vast majority of people who aren’t involved in IT, I’d still say that the “waiter” meaning of “server” would be more common. It isn’t only expensive restaurants that use “server” with that meaning; it’s also used in affordable places, too. “Hi, I’m Anna, I’ll be your server tonight. What can I get you to drink?”
The dictionaries do contain the word banfhreastalaí but a quick search for that term shows that most of the hits are from dictionaries and grammar sites, suggesting that it's a word that's included for the sake of completeness, rather than because it is actually used.
Other such ban words have been officially dropped - the rank of Bangharda no longer exists, and Altra is now the preferred term for Nurse, even though the FGB has an entry for banaltra with banaltra fir for "male nurse". The Nursing and Midwifery Board of Ireland is An Bord Altranais agus Cnáimhseachais na hÉireann