Hatcher, a defensive end who finished with 13 tackles and 27 quarterback pressures, signed a second-round tender worth $1.759 million.
Siavii, a nose tackle who had 11 tackles in a backup role behind All-Pro Jay Ratliff, signed his original-round tender worth $1.226 million.
The Cowboys offered tender deals to 11 of their 13 restricted free agents. Four have signed. The deadline for restricted free agents to sign offer sheets is April 15.