Interesting I assumed they were Ukranian because I searched for Kuban Cossacks (as given) And the Ensemble Beryozka (men) do Cossak dances.

There has been a lot of antagonism between Russia and Cossacks over the years, including the original use of the term "holocaust".

A quick look at Russian Music and Dance still makes you think they are Russian. The DVDs are sold from Australia.

Just to muddy the waters, the Kuban region is adjacent to Crimea and Wiki makes reference to Cossack forts.

Maeve's link doesn't reveal their secret, and the spelling is yet more confusing. But it is a start.