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

No.

While the word "viu" is grammatically the same in both varieties (it is the third-person singular preterite indicative of the verb ver), there is a significant difference in typical usage. In Brazilian Portuguese, "viu" frequently functions as a conversational tag or interjection at the end of a sentence to seek confirmation, emphasize a point, or mean "understand?", "got it?", or "do you hear me?". In Continental Portuguese, this usage is very uncommon. A person from Portugal would typically use "percebeste?" (did you understand?), "ouviste?" (did you hear?), or "estás a ver?" (you see?) to achieve the same communicative effect.

Brazilian Portuguese Examples:

1. "Não esquece a chave, viu?" (Don't forget the key, okay?)
2. "Você viu onde eu deixei meu celular?" (Did you see where I left my cell phone?)
3. "Não faz isso de novo, viu?" (Don't do that again, got it?)
4. "Ele viu o filme ontem à noite." (He saw the movie last night.)
5. "Eu já te falei isso, viu?" (I already told you that, you hear me?)

Continental Portuguese Examples:

1. "Não te esqueças da chave, percebeste?" (Don't forget the key, understand?)
2. "Viste onde deixei o meu telemóvel?" (Did you see where I left my mobile phone?)
3. "Não faças isso outra vez, ouviste?" (Don't do that again, do you hear?)
4. "Ele viu o filme ontem à noite." (He saw the movie last night.)
5. "Eu já te disse isso, estás a ver?" (I already told you that, you see?)