The ww1 winter Russians could be used, with an headswap, for late ww2 (from 1943 onwards)soviet soldiers in greatcoats. (This because of their shoulder plates. Abolished during the revolution, but reintroduced in early 1943. So from Karakov to Berlin, these figures can be used as Russians, but note that the figures with the non-integral hood, the bashlyk need some rework, for this was an ww1 item.) Btw, with some headswaps these figures could also serve as ww1 Serbs and Bulgarians I think.
Anything is possible, but ... have a look at http://rkkaww2.armchairgeneral.com/uniform/uniform1.htm and following pages has a few drawings that show them in more Hungarian???/German influenced helmets (I do recall seeing some Eastern European infantry in these helmets, but can't recall which) just prior to WW2.
Those German looking helmets were the 1936 model, and discarded in 1941 to be and replaced by the 'classic' soviet helmet 1941. During the first months of operation Babarossa this old 1936 helmet was still worn.
Some Baltic states used mainly German equipment, But Romania, Tsechoslovakia and Poland all used other types of helmets. The Romanians used the French Adrian just prior to the world war, and some service troops were still equipped with them in 1941. Hungary had German helmets I think.