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

Yes

The spelling, meaning, and grammatical function of "oitenta" are identical in both Brazilian and Continental Portuguese. The only difference lies in pronunciation.

In Brazilian Portuguese, the vowels tend to be more open and clearly articulated, following a syllable-timed rhythm. In Continental Portuguese, the pronunciation is more stress-timed, meaning unstressed vowels (like the "e" in the middle of "oitenta") are often reduced, shortened, or almost silent, making the word sound more "clipped" to a Brazilian ear.

Brazilian Portuguese Examples

1. Eu tenho oitenta reais no bolso. (I have eighty reais in my pocket.)
2. Minha avó já está com oitenta anos. (My grandmother is already eighty years old.)
3. Oitenta por cento dos alunos passaram na prova. (Eighty percent of the students passed the test.)
4. O preço desse celular é de oitenta reais. (The price of this cell phone is eighty reais.)
5. Ele correu oitenta metros em poucos segundos. (He ran eighty meters in a few seconds.)

Continental Portuguese Examples

1. O autocarro custa oitenta cêntimos. (The bus costs eighty cents.)
2. A minha avó já tem oitenta anos. (My grandmother is already eighty years old.)
3. Oitenta por cento da turma aprovou o projeto. (Eighty percent of the class approved the project.)
4. O preço deste telemóvel é de oitenta euros. (The price of this mobile phone is eighty euros.)
5. Ele correu oitenta metros num instante. (He ran eighty meters in an instant.)