А так ?
if (!empty($res['logo']))
echo '<img src="/manager/logo/small' . $res['logo'] . '" alt=""/> ';
elseif (!empty($arr['union_team']))
echo '<img src="/images/union/' . $arr['union_team'] . '.jpg" alt=""/>';
else
echo '<img src="/manager/logo/smallnologo.jpg" alt=""/> ';