Russian is one of the main Barrayaran languages resulted from the primary settlement groups populated Barrayar. Other main languages are English, French and Greek. Judging by the Vorkosigan books, English and French surnames are very common among both vors and non-vors. Unlike them, Russian surnames are very rarely mentioned (Greek surnames are rare too, but it's due to that Greek was the smallest group, Russian was the biggest, or one of biggest).
I can remember only one Russian-like surname referring to a vor - (Vor)drozda (BTW I'm not sure Bujold meant it to be Russian).
Meanwhile there are many Russian forenames among vors. Almost every vor house has at least one member having Russian forename, e.g: Youri and Serg Vorbarra, Piotr Vorkosigan, Ivan Vorpatril.
So what is the reason of rarity of Russian surnames?
Does it mean that Barrayar has been ruled by Western Europeans at the beginning of the Time of Isolation?