Those would be "captive" ferrets, not "domesticated" ones. (They want to introduce the offspring from the breeding program into the wild, and have in fact done this for about 10,000 offspring.)

This article in Science about the first cloned black-footed ferret (https://www.science.org/content/article/conservation-first-c...) specifically says, "Cloning endangered species faces unique ethical questions, as well. One is whether the clone, which can hold trace DNA from its surrogate mother, is actually the same as the species that researchers are trying to save. For example, black-footed ferret clones are created using eggs from domestic ferrets, meaning they carry that species’ mitochondrial DNA, which is left in the egg after its nucleus is extracted."

(Later in the article: "... apart from her mitochondrial DNA, most of which comes from her domestic mother, genetic analysis shows she is 100% a blackfooted ferret".)

"Domestic ferret" refers to the domesticated European polecat (e.g., https://www.inaturalist.org/taxa/399272-Mustela-furo).