I was looking for the code responsible for placing an underscore in front of python dictionary keys and was thinking that might be it. But, I have found a way to rename the key within Matlab so that it conforms to struct naming conventions:

try
    matObj = struct(pyObj);
catch ME
    if strcmp(ME.identifier, 'MATLAB:Cell2Struct:InvalidFieldName')
        offending_key = regexp(ME.message, '(?<=")[^"]+(?=")', 'match');
        offending_key = offending_key{1};
        pyObj{offending_key(2:end)} = pyObj.pop(offending_key);
        matObj = struct(pyObj);
    end
end