Russian Superliga open the door to 2 team from ex sovietic countries. These teams are Lokomotiv Kharkiv and Shaktar Soligorsk, from Ukraine and Bielorussia. Last season there was Minks instead of Soligorsk. Urkraine and Bielorussia still have their own championship. Lokomotiv Kharkiv, for example, is competing in national league with the team B.
This practice is not only in volleyball. The "Russian" Continental Hockey League has teams from Latvia, Belarus and even Slovakia, so it's more of an inter-state championship. It also helps these teams from the foreign countries with weaker championships and provides them with an opportunity to develop.
Thanks a lot,