The only two instances I recall the Greek minority being mentioned very particularly are in Warrior's Apprentice, when Miles has a run-in with a handful who mark him out as a mutant immediately upon arriving at Camp Permafrost, and in Civil Campaign, during one of the wedding campaign meetings, when Alys mentions infanticide among "certain language groups" in the backcountry. Which Ivan 'helpfully' translates as "greekie hicks". None of the characters with Greek names seem to display any cultural particulars.

I do find it interesting that Lois primarily identifies them as a "language group" rather than a cultural group; it suggests, in-universe, that Barrayar has a unified planetary culture while retaining four (I think) major linguistic divisions.