You can verify that the DHCP option you have created is being used for the Middle Tier address by looking for the following STRING value in the HKLM\Software\Novell\ZENworks registry key at the workstation:
MiddleTierAddress
You can change the data for this value to the Middle Tier address being delivered from DHCP. If you delete the key, it is re-created with the address in DHCP option on the next reboot.