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

Yes

The word "seis" is identical in spelling, meaning, and grammatical function in both Brazilian and European (Continental) Portuguese. The only difference is in pronunciation. In Brazilian Portuguese, the vowel sound is typically more open and the syllable is more distinct, whereas in European Portuguese, the pronunciation is often more closed and the rhythm of the word may be more shortened or "staccato" depending on the surrounding context.

Brazilian Portuguese Examples

1. São seis horas da manhã. (It is six in the morning.)
2. Eu comprei seis laranjas na feira. (I bought six oranges at the market.)
3. O meu filho tem seis anos. (My son is six years old.)
4. O show vai começar às seis. (The show is going to start at six.)
5. Tem seis pessoas na sala. (There are six people in the room.)

European Portuguese Examples

1. São seis horas da manhã. (It is six in the morning.)
2. Comprei seis laranjas no mercado. (I bought six oranges at the market.)
3. O meu filho tem seis anos. (My son is six years old.)
4. O concerto vai começar às seis. (The concert is going to start at six.)
5. Há seis pessoas na sala. (There are six people in the room.)