They couldn't use "bhfota" because "bhf-" is only used as eclipsis for "f-".
In fact, apart from mutations and a few words like "bhur", the /v/ sound never occurs at the beginning of a word in Irish. Words that begin with /v/ are already noticeably foreign, so they may as well write them with a "v". Kind of like how nobody minds writing "xylophone" with an "x"!
My pocket dictionary has around 50 Irish words beginning with V, eight Irish words beginning with J, as well as wigwam, xileafón, yóyó, and zú. In 1922, the English-Irish Phrase Dictionary included the following in its preface:
There can be no doubt but that the English language has influenced for fully a century past the language of native Irish speakers, even of those who know no English. To condemn all Irish that bears traces of such influence would be severe, and in many ways harmful. As far as possible, however, English turns of expression have been avoided in this book.
Anglicisms are not a new feature in Irish, although sometimes they have replaced older native forms (e.g. modern Véineas vs. mediæval Uenir for the goddess and the planet, both ultimately derived from Latin). Note that béarlachas (“anglicism”) is singular; its plural is béarlachais.
feoilséantóir is not the Irish for "vegetarian". feoilséantóir is a person who abstains from meat for penitential purposes, and is a far older word than the 19th century "vegetarian". As vegetarians don't abstain from meat as a penance, but instead make what they consider to be a positive choice, many of them consider feoilséantóir inappopriate. If you give up eating meat for Lent, you're a feoilséantóir, not a veigeatóir.
There is a difference between "vegetarian" and "vegan".
The 1959 English Irish dictionary (de Bhaldraithe) doesn't have any entry for "vegan", and for vegetarian offers feoilséantach as an adjective (a vegetarian menu) and feoilséantóir as a masculine noun. The 1977 Foclóir Gaeilge-Béarla (Ó Dónaill) offers some additional information on the plural and genitive forms of feoilséantóir. There isn't any entry for veigeán.