Is the word aniversariante the same in Brazilian and European Portuguese?

Yes

The word "aniversariante" is identical in both Brazilian and Continental Portuguese in terms of meaning, spelling, and grammar. The only significant difference lies in pronunciation and the syntactic context in which it is typically placed.

In Brazil, the final "e" is almost always pronounced as a clear /i/ (like the "ee" in "see"). In Portugal, the final "e" is a "reduced" or "vocalized" vowel, sounding much more closed and almost swallowed (/ɨ/). Additionally, while the word itself is the same, the surrounding sentence structure will differ: Brazilians naturally use the gerund (e.g., está ficando), whereas Portuguese people naturally use the preposition "a" followed by the infinitive (e.g., está a ficar).

Brazilian Portuguese Examples

1. O aniversariante está muito animado com a festa. (The birthday person is very excited about the party.)
2. Fizemos um bolo especial para o aniversariante. (We made a special cake for the birthday person.)
3. O aniversariante esqueceu de trazer o presente. (The birthday person forgot to bring the gift.)
4. Queremos dar parabéns ao aniversariante. (We want to say happy birthday to the birthday person.)
5. O aniversariante está ficando mais velho hoje! (The birthday person is getting older today!)

Portuguese (Continental) Examples

1. O aniversariante está muito contente com a festa. (The birthday person is very happy with the party.)
2. Fizemos um bolo especial para o aniversariante. (We made a special cake for the birthday person.)
3. O aniversariante esqueceu-se de trazer o presente. (The birthday person forgot to bring the gift.)
4. Queremos dar os parabéns ao aniversariante. (We want to say happy birthday to the birthday person.)
5. O aniversariante está a ficar mais velho hoje! (The birthday person is getting older today!)