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

Yes

The spelling, meaning, and grammatical function of "viúvo" are identical in both Brazilian and Continental Portuguese. The only difference is pronunciation. In Brazilian Portuguese, the vowels are generally more open and the rhythm is more "syllable-timed," making the word sound more melodic. In Continental Portuguese, the vowels are more closed and there is a stronger tendency to reduce or "swallow" unstressed vowels, which can make the word sound more clipped or shortened.

Brazilian Portuguese Examples

1. Ele é viúvo há cinco anos. (He has been a widower for five years.)
2. Meu vizinho é um senhor viúvo. (My neighbor is a widower.)
3. Ele ficou viúvo muito jovem. (He became a widower very young.)
4. O homem viúvo mora sozinho. (The widower lives alone.)
5. Ele é viúvo e muito dedicado aos filhos. (He is a widower and very dedicated to his children.)

Continental Portuguese Examples

1. Ele é viúvo há cinco anos. (He has been a widower for five years.)
2. O meu vizinho é um senhor viúvo. (My neighbor is a widower.)
3. Ele ficou viúvo muito jovem. (He became a widower very young.)
4. O homem viúvo mora sozinho. (The widower lives alone.)
5. Ele é viúvo e muito dedicado aos filhos. (He is a widower and very dedicated to his children.)