Neither one of them are ready to be on the major league team until AT LEAST September. Dunning has 11 starts at AA and Cease had 10. Cease's career high in IP is also 124. Santana is a spaceholder so we don't have to rush anyone decent.
The Sox don't view Stephen's or Guerrero as anything and neither does MLB. Otherwise they would have been protected in the Rule 5 draft and/or someone would have picked them as high MiLB pitchers.
Wading through all of this, this is the most important thing here. Who knows, if they can turn Santana into a fifth starter and get anything for him at the break, they will have won.