Are these commas placed correctly?

The original sentence is correct.

The appositive which modifies Gu Kulai is the entire phrase "wife of a Chinese politician at the center of a major scandal". You do not need a comma anywhere in that phrase, and it would be incorrect to add one. It is, however, correct to add a comma at the end of the appositive, which is exactly what we see above.

It appears from glancing news articles that her husband the politician is considered the center of scandal, so the first phrase is correct without the comma.

The second phrase would not benefit from a comma. Consider a different example:

She denied murdering a British man during a business meeting on Tuesday.

She denied murdering a British man, during a business meeting on Tuesday.

What happened during the business meeting on Tuesday - a murder or a denial? Neither sentence gives you any clue, and the comma doesn't help. In fact, in the second example it feels flat out unnatural.

The phrase in the original sentence seems pretty clear to me given the context. But if you were worried about ambiguity, it would be necessary to reword the sentence, not chuck in extra commas.

Whether or not a comma is necessary after "wife of a Chinese politician" depends on the facts of the case.

"Gu Kailai, wife of a Chinese politician at the centre of a major scandal" means that there is a Chinese politician at the centre of a major scandal, and Gu Kailai is his wife.

"Gu Kailai, wife of a Chinese politician, at the centre of a major scandal" means that Gu Kailai is at the centre of a major scandal, and is the wife of a Chinese politician.

The second half of the sentence is common newspaperese...

Smith denied murdering a man at Guildford Crown Court

meaning he uttered the denial at Guildford Crown Court, rather than that the murder occurred at Guildford Crown Court and Smith denied it somewhere else.