I've now read Radkey's book and can hopefully answer some questions based on it.
Is that a Tatar regionalist party I see there - the bit of light green in a sea of orangey-brown?
The Socialist Revolutionaries were the largest party here, but with only 31%. Ethnic lists did well. A Chuvash list won 26%, left-wing Tatars won 18%, and right-wing Tatars won 12%. I didn't see anything about Mari lists, but since data are often missing in this election, you never know.
Karelia also seems odd, and I can't vouch for the accuracy of the results there on the map; another source I saw put the SRs victorious there.
This is Olonets Governorate, which had an odd voting system. Instead of lists, every voter had two votes to elect individuals; it might have worked like the two-member seats in pre-1950 UK general elections, and should probably be interpreted in the same way. The Socialist Revolutionaries and Mensheviks each stood one candidate. The SRs won votes equal to 85% of voters, the Mensheviks 84%. As Zuza wrote, way ahead of their Kadet rivals.
In sources I know those who won in green regions are labelled as "Socialists", and I can only guess what exact socialists are meant, but judging by their geography and some other things it seems they indeed were Ukrainian SRs and other regional/ethnic socialists.
Radkey says the winners in these regions were:
Menshevik: Transcaucasus
SR: Kazan, Olonets
Bolshevik: Estonia (though outpolled by all Estonian nationality parties together)
Ukrainian bloc: Ekaterinoslav, Kiev, Podolia
Ukrainian SR: Chernigov, Poltava, Volhynia (though there also seems to be a Ukrainian SR + Left Russian SR joint list in Poltava)
But in this election, there's no one, final version of the truth, because the records are too sparse.