Did Nana Visitor actually sing the song that her character sings?

Question

In an episode of Star Trek: Deep Space Nine, Odo (Rene Auberjonois) is in love with Major Kira (Nana Visitor) and does not know how to court her. He seeks advice from a character in the holodeck who is modeled on a Rat-Pack-type Vegas singer from the mid-20th Century. Over the course of the episode this singer turns in beautiful renditions of a series of songs associated with Frank Sinatra. And a hologram that resembles Major Kira (the hologram also played by Nana Visitor) sings a torch song that I cannot recall.

The male singer was played by Jack Darren as Vic Fontaine

Were these song recorded for the episode, or did they just cast a professional singer and use his album tracks for the show? Did Nana Visitor actually sing the song that her character sings, or (as I think they sometimes do in Disney films) did they use a professional singer for just the songs, with another actor appearing and performing the spoken parts?

Answer 1

Were these song recorded for the episode, or did they just cast a professional singer and use his album tracks for the show?

It was Nana Visitor singing.

Actress Nana Visitor, who began her acting career as a stage musical actress, sings "Fever" in "His Way". Visitor's performance of "Fever" was included on The Best of Star Trek, Volume Two. Visitor chose the song herself.

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After DS9 ended, Visitor had a recurring role as villain Dr. Elizabeth Renfro on the television series Dark Angel and starred as Roxie Hart in the touring and Broadway companies of the musical Chicago.

^Wikipedia

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Darren also did his own songs

In 1998, he achieved renewed popularity as a singer through his appearances on Star Trek: Deep Space Nine in the role of holographic crooner and advice-giver Vic Fontaine; many of his performances on the show were re-recorded for the album This One's from the Heart (1999). The album showed Darren, a close friend of Frank Sinatra, comfortably singing in the Sinatra style; the 2001 follow-up Because of You showed similar inspiration from Tony Bennett.

^Wikipedia