A few Leerans have been infested, but never the entire population.
Other races are briefly mentioned. A few Ongachic (the Ongachics are a nomadic race, if I recall correctly, so their entire race would never have been infested because the Yeerks couldn't hunt them all down). The Sstram and the Mak are mentioned only in book #6, never shown, and never brought up beyond that. The Garatrons were supposedly being tried as a new host race, but only one Garatron-controller ever appeared in the series.
As a final note, there was a war going on on the Anati homeworld at around the same time as the war for Earth. So I can only assume that the Anati were another host race, whose planet was at about the same stage of infestation (maybe not quite) as Earth.
Did I miss any? Good question, by the way.